Optimizing effects of organic farming and moderately low nitrogen levels on soil carbon and nitrogen pools, humus composition and related enzyme activities

Optimizing effects of organic farming and moderately low nitrogen levels on soil carbon and nitrogen pools, humus composition and related enzyme activities | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Optimizing effects of organic farming and moderately low nitrogen levels on soil carbon and nitrogen pools, humus composition and related enzyme activities Guanghua Wang, Yuanjie Chen, Yuqi Chen, Shilong Yu, Xiaomin Huang, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5163192/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract With the development of intensive agriculture, soil health issues has received widespread attention. However, the mechanism of response to soil carbon and nitrogen pool sequestration characteristics under different cultivation practices in combination with nitrogen application is not yet elucidated. This limits the idea of trying to improve the soil biosystem in paddy fields through organic cultivation combined with appropriate nitrogen reduction fertilization. A split-plot design was employed, with cultivation methods (organic cultivation [OF] and conventional cultivation [CF]) and nitrogen levels (pure nitrogen at 180 kg·hm − 2 [N12] and pure nitrogen at 270 kg·hm − 2 [N18]) combined into four treatments. The impacts of organic and conventional cultivation as well as different nitrogen fertilizer application rates on soil properties were compared. The results demonstrated that organic cultivation combined with appropriate nitrogen reduction significantly increased the total carbon content of the surface soil and significantly increased the organic carbon content in the soil. Soil ammonium nitrogen content showed an overall trend of decreasing and then increasing, while the opposite was true for soil nitrate nitrogen content. Notably, the organic cultivation increased the activity of enzymes involved in the carbon and nitrogen cycle and the content of humic acid in the tillage layer, which led to the improvement of the soil aggregate structure.This research indicates that organic cultivation combined with appropriate nitrogen reduction fertilization positively affects soil carbon and nitrogen pool characteristics. This study provides new insights for restoring soil fertility and promoting sustainable agriculture. Earth and environmental sciences/Ecology Earth and environmental sciences/Environmental sciences Organic cultivation Soil carbon and nitrogen pools Soil aggregates Humic composition Enzyme activity Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction The physicochemical properties of soil serve as crucial indicators for assessing soil health and productivity, exerting significant influences on crop growth, environmental quality, and climate change 1 . In recent years, with the development of intensive agriculture, improper cultivation practices have significantly impacted the physicochemical properties of soil. Organic cultivation and moderate reduction in nitrogen fertilization can effectively improve soil physicochemical properties, gradually ameliorating soil conditions without compromising crop yields 2 , aligning with the future trend of sustainable agriculture. Soil nitrogen pool represents the total amount of nitrogen stored in the soil. Nitrogen fertilization management practices have a significant impact on soil nitrogen pool. Due to limitations in traditional agriculture, excessive application of chemical or nitrogen fertilizers, compared to organic fertilizers, leads to a significant decrease in soil carbon-nitrogen ratio, which has become a consensus in recent years. Moderately reducing nitrogen fertilizer application can prevent land degradation, yield reduction due to nitrogen deficiency, or decreased fertilizer efficiency and environmental harm caused by excessive nitrogen fertilization. Adequate nitrogen fertilization can enhance soil nitrogen supply capacity to meet crop nitrogen demand. However, excessive nitrogen application can lead to nitrogen leaching, causing environmental pollution. Yang et al. 3 also found that organic cultivation can increase soil nitrogen supply capacity while reducing nitrogen leaching, providing theoretical support for the combination of organic cultivation and moderate reduction in nitrogen fertilizer application. Soil carbon pool refers to the total amount of organic carbon stored in the soil, which has a significant impact on global carbon balance. Even slight changes in soil carbon pool can have important effects on global carbon balance. Organic cultivation can increase soil carbon storage by increasing organic matter input into the soil. Compared with conventional cultivation, organic cultivation can increase soil organic matter content by 20–50% 4 . Increasing soil carbon storage can improve soil fertility, enhance soil structure, and mitigate climate change through carbon sequestration 5 . Current research has found that most nitrogen and organic carbon in soil aggregate in water-stable macroaggregates with particle sizes of 0.25-2 mm. Reasonable nitrogen addition can promote the formation of these aggregates, while enhancing organic carbon content within them 6 , 7 . Additionally, Thomaz et al. 8 found that 100 ~ 200 µm microaggregates are formed by the adsorption of soil microorganisms on organic residues, providing evidence for the promotion of aggregate formation by organic cultivation. Microaggregates larger than 0.05 mm have advantages in adsorbing humic acid due to their larger contact area with the external environment, promoting mineralization reactions between microorganisms and humic acid 9 . Humic acid's moderate binding characteristics enable it to form good aggregate structures with soil particles or sand particles. The proportion of humic acid to fulvic acid can effectively evaluate the quality of soil humus, serving as an important indicator for maintaining or improving soil fertility, and it is an essential component of soil nutrients 10 . Organic materials can promote the formation of soil humus, mainly by increasing the proportion and activity of humic acid in humic acid 11 . Humic acid in humus is usually considered inert matter in soil and mainly participates in the soil organic carbon cycle 12 , serving as a carbon source. During the formation of humus, mineralization of organic nitrogen and denitrification of nitrate nitrogen may lead to the production of gases such as ammonia, nitrogen, and nitrogen dioxide, affecting the process of nitrogen fixation in soil 13 . Therefore, selecting organic materials rationally is crucial to promote humus formation while controlling nitrogen volatilization reactions. The composition of soil humus is significantly influenced by natural conditions and human management activities, and studying these changes helps understand the effects of different nitrogen application rates on soil carbon cycling 14 . Q. Wang et al. 15 found that long-term excessive application of chemical fertilizers can lead to a decrease in organic carbon and humus content, exacerbating soil acidification. The combined application of chemical and organic fertilizers not only contributes to the accumulation of organic carbon and humus but also promotes the humification process of soil, improving the soil microecological environment. Numerous studies have explored the effects of returning organic materials to soil on the form and content of soil humus, but these effects are greatly influenced by soil type, climate conditions, and the amount of exogenous organic material input. In addition, different plant root exudates and residues have varying degrees of impact on soil microbial community metabolic activities and humus forms 14 . Soil enzyme activity often represents the intensity of soil microbial activity. Adopting organic cultivation measures and moderate nitrogen fertilization can promote soil microbial activity and increase the activity of various soil enzymes 16 . Among them, leucine aminopeptidase is closely related to soil nitrogen cycling 17 , and soil sucrase catalyzes the hydrolysis of sucrose in soil into monosaccharides more conducive to rhizosphere absorption 18 . By measuring the changes in the activity of these specific enzymes, the transformation rate of relevant products in the soil and the rate of nutrient synthesis can be indirectly inferred. This study focuses on organic cultivation and nitrogen application levels to systematically analyze their effects on soil physicochemical properties by investigating soil carbon storage, nitrogen supply, humus composition, and enzyme activity indicators. Previous studies have focused on nitrogen fertilizer management and cultivation methods, without in-depth research on changes in soil aggregates and humus composition. Therefore, this study is expected to provide theoretical support for the combination of nitrogen reduction fertilization and organic cultivation in planting models by examining soil physicochemical properties. Materials and Methods Experimental design The experimental field was located within the Ma Peng Wan Ecological Agriculture Co., Ltd. in Gaoyou City, Yangzhou, Jiangsu Province, China, from 2021 to 2022 (longitude 119°25', latitude 32°47'), situated in the northern subtropical monsoon humid climate zone of China. The average annual temperature is approximately 16.2°C, with an annual precipitation of about 1341.5 mm and an annual sunshine duration of around 2100 hours. The frost-free period lasts approximately 221 days. The company is located in Tayuan Village, Mapeng Town, Gaoyou City, covering an area of 135 ha. In 2011, the China Organic Food Certification Center (COFCC) granted it the organic food conversion certification and it is a modern ecological organic farm specializing in the cultivation of organic rice. The experimental field has been dedicated to organic cultivation research since 2012, with stable soil properties characterized by clay loam texture. The soil property is stable and the texture is clay loam. The soil sample collected in June 2022 contained 27.93 g·kg − 1 organic matter, 112.24 mg·kg − 1 alkali-hydrolyzable nitrogen, 7.36 mg·kg − 1 available phosphorus, 61.08 mg·kg − 1 available potassium, and 1.31 g·kg − 1 total nitrogen. The pH of the sample was 8.13. Test materials This experiment utilized high-yield rice varieties commonly grown in the middle and lower reaches of the Yangtze River, namely Nanjing 46 (Nanjing46, Japonica ), with a full growth period of 165 days, and Huai Fragrant Jing 15 (Huaixiangjing15, Japonica ), with a full growth period of 150 days. Tillage practices The experimental plots were designed using a split-plot design, with planting methods (organic planting, conventional planting) as the main plots and nitrogen input levels during the rice season (180, 270 kg/hm²) as the subplots, with an area of 49 m² (7 m × 7 m) each, replicated three times. Purple clouds were planted as the previous crop, and the test rice was sown on May 18, 2022, with manual transplanting on June 9, using a spacing of 0.3 m × 0.125 m, with 3 seedlings per hill. The main plots of planting methods were distributed in adjacent fields with similar fertility, separated by ridges, and isolated between subplots with small ridges, covered with plastic film to ensure separate irrigation and drainage for each subplot. Conventional cultivation (CF) followed local practices for high-yield cultivation management in Gaoyou, with 45% compound fertilizer (containing 15% nitrogen) applied as base fertilizer one day before rice transplanting. Urea was applied as topdressing fertilizer in three installments: first tillering, second tillering, and heading. Management measures for disease, pests, and weeds were implemented according to conventional cultivation requirements. Organic cultivation (OF) was managed according to the national standards for organic product production (GB/T19630.1), adopting the milk vetch-rice planting pattern. Milk vetch (containing 0.33% nitrogen) were plowed and applied as base fertilizer two weeks before rice transplanting. Rapeseed cake (containing 4.60% nitrogen) and bio-organic fertilizer (containing 4.00% nitrogen) were applied as base fertilizer one day before rice transplanting, with bio-organic fertilizer applied as topdressing fertilizer in mid-July as heading fertilizer. N18 equivalent to pure nitrogen 270 kg·hm − 2 (conventional nitrogen application by local farmers) and N12 equivalent to pure nitrogen 180 kg·hm − 2 (nitrogen reduction treatment in the experiment). Specific fertilization strategies are shown in Table 1 . Organic rice production throughout the process complies with organic rice production management regulations, with disease and pest control exclusively using certified organic pesticides, and manual weeding in the plots. After two years of the above-mentioned cultivation and fertilization management positioning, the experimental plots focused on soil research in 2022. Table 1 Fertilization rate under organic and conventional cultivation nitrogen levels (kg·hm − 2 ) Cultivate Way Nitrogen application level Total Basal fertilizer Topdressing fertilizer Compound fertilizer(15%N) Milk vetch(0.33%N) Rapeseed cake(4.6%N) Bio-organic fertilizer(4%N) Urea(46%N) Bio-organic fertilizer(4%N) CF N12 180 500 / / / 229 / N18 270 750 / / / 343 / OF N12 180 / 12000 1200 1200 / 930 N18 270 / 12000 2400 1200 / 1800 The nutrient contents of various fertilizers are: compound fertilizer: 15%N, 15% P 2 O 5 and 15% K 2 O; Milk vetch: 0.33% N, 0.08% P 2 O 5 and 0.23% K 2 O; Rapeseed cake: 4.60% N, 0.80% P 2 O 5 , 1.04% K 2 O, 0.80% Ca, 0.48% Mg and various trace elements; Bio-organic fertilizer: 4.00% N, 1.87% P 2 O 5 , 2.28% K 2 O, Various organic acids, peptides and rich nutrient elements including 53% organic matter. Soil sample collection Soil samples were collected using a soil sampler at the tillering stage, heading stage, and maturity stage of rice growth, following a five-point sampling method. Soil samples were taken from depths of 0–10 cm (surface layer) and 10–20 cm (subsurface layer) in each plot. After uniformly mixing the soil samples from each plot, plant roots and stones were removed, and a portion of the samples was stored in sealed bags and placed in a -70°C freezer as fresh samples for subsequent determination of soil active carbon and nitrogen. The remaining soil samples were air-dried completely and sieved through a 100-mesh sieve for further analysis. Additionally, at the maturity stage, soil aggregates were collected in the field using a shovel (with the premise of not disturbing the original soil structure) for aggregate determination. Determination of soil nutrient content Soil total nitrogen was determined using the semi-micro Kjeldahl method, soil organic matter was determined using the potassium dichromate heating external heating method, and soil alkali-hydrolyzable nitrogen was determined using the alkali diffusion method 19 . Determination of soil enzyme activity For air-dried soil samples at the maturity stage of rice, soil sucrase, soil cellulase, and soil leucine aminopeptidase activities were determined separately. Soil sucrase activity was determined using the 3,5-dinitrosalicylic acid colorimetric method 20 , with enzyme activity expressed as the amount of glucose produced per gram of soil after 1 day; soil cellulase activity was determined using the anthrone colorimetric method 21 , with enzyme activity expressed as the amount of glucose produced per gram of soil after 1 day; soil leucine aminopeptidase activity was determined using the p-nitroaniline colorimetric method 22 , with enzyme activity expressed as the amount of p-nitroaniline produced per gram of soil after 1 day. Determination of soil active carbon and nitrogen indices For air-dried soil samples at the tillering stage, heading stage, and maturity stage of rice, soil organic carbon was determined using the low-temperature external heating potassium dichromate oxidation-colorimetric method 23 . The TOC-L CPH total organic carbon analyzer was used to determine soil total carbon, inorganic carbon, and soluble organic carbon in air-dried soil samples at the tillering stage, heading stage, and maturity stage of rice 24 . Ammonium nitrogen and nitrate nitrogen were determined using a continuous flow analyzer (Proxima) after extraction with 1 mol·L − 1 KCl solution from air-dried soil samples at the tillering stage, heading stage, and maturity stage of rice. Acid hydrolysis method was used to determine acid hydrolyzable organic carbon according to the method of Rovira and Vallejo 25 . Determination of soil aggregates The wet sieving method 26 was used to determine water-stable aggregates. Samples were taken at the maturity stage, and fresh soil was retrieved from the field using a shovel (with the premise of not disturbing the original soil structure). Soil samples were split along the soil sample gaps, removing residual broken stems, roots, stones, and other impurities. The samples were turned every 3–4 hours, and the soil samples were continuously split along the gaps until the soil samples could be directly crushed by hand rather than flattened when pinched. The soil samples were processed in this manner and air-dried to a moisture content slightly below 10% for analysis. Initially, 10 g of soil sample was dried to a constant weight to calculate the moisture content. Subsequently, 50 g of soil sample was placed in a vibrating mechanical sieve shaker, subjected to vertical oscillation with an amplitude of 3 cm and a duration of 30 minutes for wet sieving. The soil samples separated in five sieves (2 mm, 1 mm, 500 µm, 250 µm, 106 µm) were transferred and dried at 50°C. The proportion of aggregates of different particle sizes in the soil was calculated based on the moisture content and the dry weight of the soil samples in different sieves. Determination of soil humus content Soil humus content was determined using the modified humus composition method 27 on air-dried soil samples collected at the maturity stage of rice. Data analysis methods Microsoft Excel 2021 and SPSS 23.0 software were used for data organization and analysis, with Origin 2022 used for graphical representation. Data from each treatment (cultivation method and nitrogen level combination) were subjected to one-way analysis of variance (ANOVA), and LSD (Least Significant Difference) was used to compare differences in the data. Results Soil organic carbon The organic carbon content of soil surface and subsurface under different planting systems and nitrogen levels at three sampling stages is shown in Fig. 1 . Overall, soil organic carbon is influenced by the interaction between cultivation methods and nitrogen levels, with significantly higher levels in the soil surface compared to the subsurface. During the tillering and heading stages, the organic carbon content in the soil surface is significantly higher under certain cultivation methods and nitrogen levels, with CFN18 and OFN12 exhibiting the highest organic carbon content. In the subsurface, there is no significant pattern, and differences between treatments are minimal. During the tillering stage, the organic carbon content in the soil surface is significantly higher in OFN12 compared to CFN12, and in CFN18 compared to OFN18; however, these differences diminish during the heading stage, with increases of 7.42% and 8.12%, respectively. During the maturity stage, the organic carbon content in the soil surface is significantly higher in OFN12 treatment compared to other treatments. These results indicate that CFN18 or OFN12 treatments can increase the organic carbon content in the soil surface during the tillering stage, with the increase from CFN18 treatment gradually diminishing as the growth progresses, disappearing by the maturity stage. The organic carbon content in the subsurface soil is minimally affected by treatments. OFN12 treatment consistently results in higher organic carbon content in both soil layers and across all stages, promoting rice growth. Soil Carbon Pool The content and variance analysis of soil total carbon components under two nitrogen levels in organic and conventional cultivation at three sampling periods are presented in Table 2 . Overall, the total carbon content at different periods is higher in the soil surface compared to the subsurface. Differences between treatments are primarily observed in the surface soil during the tillering stage and the subsurface soil during the maturity stage, with no significant differences during the heading stage. During the tillering stage, the total carbon content in the surface soil is mainly influenced by the interaction between cultivation methods and nitrogen levels. Specifically, the total carbon content in CFN18 treatment is 41.07% higher than that in OFN18 treatment, and 22.51% higher in OFN12 treatment compared to CFN12 treatment, with both differences being significant. In the surface soil during the maturity stage, total carbon is influenced by cultivation methods, with OFN > CF, and differences between treatments are not significant. In the subsurface soil during the maturity stage, total carbon is significantly influenced by the interaction between cultivation methods and nitrogen levels, showing a pattern opposite to that of the surface soil during the tillering stage, with higher total carbon content observed in CFN12 and OFN18 treatments compared to other treatments. In summary, OFN12 treatment can increase the total carbon content in the surface soil during all three periods, while CFN12 and OFN18 treatments increase the total carbon content in the subsurface soil. Overall, the soluble organic carbon content in the soil surface was significantly higher than that in the subsurface during all three periods, with the largest difference observed during the maturity stage. In the OF treatment during the maturity stage, the difference in soluble organic carbon content between different soil layers was the greatest (Table 2 ). The pattern of soil soluble organic carbon was highly consistent across all three periods, with OF > CF observed except in the subsurface during the maturity stage. Taking the surface soil during the maturity stage as an example, under N12, the OF treatment increased the soluble organic carbon content by 37.22% compared to CF treatment; under N18, this increase was 42.89%, both significant. Additionally, in the surface soil under the OF treatment, the soluble organic carbon content was higher under N18 than N12, with a difference of 12.41% during the maturity stage, which was significant. These findings indicate that OF significantly increases soil soluble organic carbon content, with the greatest increase observed in the surface soil during the maturity stage. In organic cultivation, the effect of increasing soluble organic carbon content is better under N18 compared to N12, particularly evident during the maturity stage. The organic carbon content in the surface soil was higher than that in the subsurface. Differences among treatments were mainly observed in the surface soil during all periods (Table 2 ). The content of acid hydrolysis organic carbon in the surface soil gradually increased after the tillering stage; after the heading stage, there was still a slight increase in the OF treatment, while a decrease was observed in the CF treatment. After the heading stage, there were no significant differences in the content of acid hydrolysis organic carbon among treatments in the subsurface soil. Across all three periods, the content of acid hydrolysis organic carbon in both soil layers was significantly influenced by cultivation methods, showing OF > CF, with significant differences. Additionally, influenced by nitrogen levels, it exhibited N18 > N12. During the maturity stage, the difference in acid hydrolysis organic carbon content in the surface soil under different cultivation methods was the greatest. Under N18, the OF treatment increased the content of acid hydrolysis organic carbon by 41.02% compared to CF, and under N12, this increase was also 38.71%. In summary, OF significantly increases the content of soil acid hydrolysis organic carbon, particularly evident in the surface soil during the maturity stage. Additionally, N18 promotes the increase in acid hydrolysis organic carbon content. Table 2 Effects of two nitrogen levels on soil carbon fractions under organic and conventional cultivation Soil layer (cm) Treatment TOC (g/kg) DOC (g/kg) (AOC) (g/kg) TS HS MS TS HS MS TS HS MS 0–10 cm CFN12 20.88 ± 0.03b 25.43 ± 0.42a 25.16 ± 0.79a 82.75 ± 3.65b 102.35 ± 2.95b 101.30 ± 3.00c 6.76 ± 0.06ab 7.64 ± 0.19b 6.29 ± 0.21b CFN18 24.18 ± 0.83a 28.45 ± 0.71a 25.84 ± 0.53a 93.20 ± 3.10b 102.55 ± 1.75b 109.70 ± 0.80c 6.21 ± 0.34b 7.84 ± 0.07b 6.69 ± 0.11b OFN12 25.58 ± 0.18a 26.02 ± 0.46a 27.64 ± 0.78a 135.90 ± 3.20a 122.30 ± 2.00a 139.45 ± 1.35b 7.14 ± 0.22ab 8.40 ± 0.30ab 8.87 ± 0.20a OFN18 17.14 ± 0.46c 26.48 ± 0.58a 27.48 ± 0.08a 142.25 ± 3.65a 129.55 ± 1.25a 156.75 ± 0.85a 7.62 ± 0.07a 8.97 ± 0.04a 9.28 ± 0.12a 10–20 cm CFN12 19.50 ± 0.16a 20.50 ± 0.39a 19.18 ± 0.10a 60.45 ± 3.65c 53.25 ± 0.05b 73.25 ± 3.05a 4.93 ± 0.16c 6.00 ± 0.07b 6.03 ± 0.09b CFN18 18.78 ± 0.66a 19.02 ± 0.91a 14.24 ± 0.55b 70.15 ± 2.15bc 67.35 ± 1.65b 71.80 ± 2.40a 5.66 ± 0.34bc 6.23 ± 0.04b 6.35 ± 0.11ab OFN12 18.69 ± 0.03a 19.28 ± 0.28a 14.46 ± 1.10b 82.90 ± 0.00ab 75.15 ± 0.25a 71.40 ± 0.15a 6.71 ± 0.19ab 6.70 ± 0.11ab 6.50 ± 0.25ab OFN18 19.99 ± 0.30a 18.84 ± 0.64a 18.82 ± 0.66a 87.85 ± 1.75a 72.50 ± 2.10a 70.40 ± 1.55a 6.94 ± 0.12a 7.39 ± 0.21a 6.94 ± 0.08a 0–10 cm F 5.92 1.55 11.08* 224.64** 127.21** 595.74** 18.51* 27.18** 245.13** N 28.35** 9.90* 0.18 6.07 3.2 54.21** 0.03 4.45 6.1 F×N 148.57** 5.33 0.47 0.36 2.87 6.5 6.22 1.07 0 10–20 cm F 0.29 1.33 0.01 76.74** 101.66** 0.22 47.86** 53.39** 12.73* N 0.6 2.51 0.17 10.22 18.22 0.12 4.63 13.32* 6.65 F×N 7.41 0.72 44.26** 1.07 38.98** 0 1.25 3.27 0.15 The data is presented as mean ± SD. Different lowercase letters within the same column indicate significant differences (p < 0.05) among the four treatments. TOC, Soil total carbon; DOC, Soil dissolved organic carbon; AOC, Soil acid hydrolysis organic carbon. TS, Tillering stage; HS, Heading stage; MS, Maturing stage; F, Cultivation pattern; N, Nitrogen application level; F × N, Interaction between cultivation mode and nitrogen level. Soil nitrogen pool As shown in Table 3 , total nitrogen content in soil surface is significantly higher than subsurface during all three periods. Differences between treatments are evident in tillering and heading stages but disappear in maturity stage. Under same nitrogen level, surface and subsurface total nitrogen is influenced by cultivation methods. Tillering stage shows OF > CF; pattern reverses after tillering. After tillering, total nitrogen in different layers is influenced by nitrogen levels. After tillering, under same cultivation method, N12 treatment increases total nitrogen in surface soil. For example, at heading stage, OFN18 total nitrogen is 14.22% higher than OFN12 in surface soil; conversely, OFN12 in subsurface soil is 23.33% higher than OFN18. Overall, alkali-hydrolyzable nitrogen content in soil surface is much higher than subsurface. Its content is influenced by various factors during different periods. At tillering stage, surface alkali-hydrolyzable nitrogen is influenced by nitrogen levels (N12 > N18). Under CF and OF, N12 treatment has 11.69% and 34.88% higher content than N18 treatment in surface soil respectively, with significant difference under OF. No significant differences in subsurface. At heading stage, no significant differences in surface; subsurface shows N12 > N18. At maturity stage, alkali-hydrolyzable nitrogen is mainly influenced by cultivation methods. N12 significantly increases soil alkali-hydrolyzable nitrogen before maturity stage. OFN12 shows more significant increase. Soil ammonium nitrogen is significantly influenced by cultivation methods, nitrogen levels, and their interaction (Table 4 ). Surface soil and N12 treatment in subsurface show trend of initially decreasing then increasing ammonium nitrogen content, especially at tillering stage. Differences between soil layers only at tillering stage. At maturity stage, due to interaction, CFN12 and OFN18 treatments have higher ammonium nitrogen content. In subsurface soil, compared to CFN18 treatment, CFN12 shows 46.97% increase; compared to OFN18 treatment, it shows 55.36% increase. Compared to surface soil, nitrate nitrogen content in subsurface shows less fluctuation (Table 4 ). At tillering stage, CFN12 and OFN18 treatments have higher nitrate nitrogen content but lose advantage after tillering. After heading stage, high nitrogen levels promote nitrate nitrogen. Surface soil shows N18 > N12. During heading and maturity stages, under conventional and organic cultivation, N18 treatment has higher nitrate nitrogen content than N12 treatment. Data indicates CFN12 and OFN18 are advantageous at tillering stage; after tillering, nitrate nitrogen in surface soil increases with nitrogen input. Table 3 Effects of two nitrogen levels on soil nitrogen fractions under organic and conventional cultivation Soil layer (cm) Treatment Soil total nitrogen (STN) (g/kg) Soil alkali-hydrolyzable nitrogen (SAN) (g/kg) Soil nitrate nitrogen NO 3 − (mg/kg) Soil ammonium nitrogen NH 4 + (mg/kg) TS HS MS TS HS MS TS HS MS TS HS MS 0-10cm CFN12 2.44 ± 0.03a 2.19 ± 0.01b 2.20 ± 0.02a 173.27 ± 3.26ab 164.78 ± 3.10a 178.91 ± 1.90b 1.00 ± 0.01c 0.76 ± 0.00a 1.18 ± 0.02b 20.03 ± 0.33a 17.67 ± 0.03b 15.45 ± 0.07b CFN18 2.05 ± 0.01b 2.11 ± 0.02b 2.41 ± 0.01a 155.14 ± 1.14b 172.34 ± 7.61a 178.12 ± 1.99b 2.27 ± 0.00a 0.63 ± 0.02a 0.69 ± 0.00c 16.74 ± 0.11b 19.85 ± 0.53a 17.85 ± 0.11a OFN12 2.20 ± 0.07ab 2.25 ± 0.07b 2.31 ± 0.10a 198.48 ± 10.48a 172.83 ± 3.07a 182.05 ± 1.30ab 2.24 ± 0.04a 0.41 ± 0.00b 0.60 ± 0.00d 16.34 ± 0.00b 16.24 ± 0.20b 15.37 ± 0.13b OFN18 1.92 ± 0.07b 2.57 ± 0.01a 2.43 ± 0.03a 147.15 ± 7.59b 163.06 ± 3.54a 191.19 ± 2.13a 1.43 ± 0.00b 0.50 ± 0.02b 1.48 ± 0.01a 19.03 ± 0.42a 19.69 ± 0.10a 17.05 ± 0.52a 10-20cm CFN12 1.28 ± 0.01a 1.29 ± 0.01b 1.54 ± 0.03a 110.68 ± 0.38a 131.26 ± 1.21ab 111.99 ± 0.96c 0.82 ± 0.02a 0.69 ± 0.01a 0.97 ± 0.01a 17.52 ± 0.15ab 17.49 ± 0.16a 16.67 ± 0.12a CFN18 1.31 ± 0.00a 1.23 ± 0.04b 1.42 ± 0.04a 113.33 ± 1.53a 115.42 ± 4.38c 127.78 ± 0.90a 0.60 ± 0.04bc 0.56 ± 0.01a 0.47 ± 0.01d 17.27 ± 0.22b 16.10 ± 0.68a 16.70 ± 0.31a OFN12 1.18 ± 0.04a 1.58 ± 0.01a 1.62 ± 0.10a 116.77 ± 0.89a 141.15 ± 1.38a 116.75 ± 0.37b 0.70 ± 0.01ab 0.24 ± 0.00a 0.66 ± 0.00c 17.06 ± 0.50b 17.54 ± 0.08a 16.53 ± 0.01a OFN18 1.31 ± 0.01a 1.28 ± 0.06b 1.50 ± 0.03a 117.09 ± 2.70a 117.77 ± 2.36bc 105.17 ± 0.06d 0.55 ± 0.01c 0.87 ± 0.01a 0.87 ± 0.01b 19.73 ± 0.64a 16.88 ± 0.51a 16.52 ± 0.47a 0-10cm F 13.34* 56.10** 1.4 1.65 0.02 19.05* 85.71** 410.83** 69.42** 6.49 7.62 2.6 N 40.60** 12.29* 10.72* 26.90** 0.05 5.07 110.23** 1.98 255.01** 1.21 95.511** 54.607** F×N 1.2 33.84** 0.73 6.15 3.36 7.14 2306.38** 94.260** 3107.97** 119.832** 4.88 1.72 10-20cm F 3.36 20.93* 1.93 9.22* 5.33 170.98** 13.53* 70.89** 23.45** 5.53 0.95 0.29 N 11.36* 23.81** 4.45 0.84 54.70** 9.51* 67.70** 858.12** 268.84** 8.059* 5.72 0 F×N 4.28 11.26* 0 0.52 2.02 402.08** 3.41 1985.11** 1619.28** 11.738* 0.71 0 The data is presented as mean ± SD. Different lowercase letters within the same column indicate significant differences (p < 0.05) among the four treatments. TS, Tillering stage; HS, Heading stage; MS, Maturing stage; F, Cultivation pattern; N, Nitrogen application level; F × N, Interaction between cultivation mode and nitrogen level. Soil humus During the tillering stage, the proportion of humic acid organic carbon content in soil humus is higher compared to other stages, ranging from 39.25–75.87% (Fig. 2 ). After the tillering stage, organic carbon is mainly provided by humin, accounting for 52.93–71.65%, which is notably significant in the 0–10 cm soil layer. In the 0–10 cm soil layer during the heading and maturity stages, compared to OFN18, the carbon content of humin in OFN12 is significantly increased by 13.36% and 17.78%, respectively, with significant differences observed. The fulvic acid content shows relatively minor fluctuations overall. The decrease in the proportion of humic acid carbon content after the tillering stage, compared to the tillering stage, is mainly due to the substantial increase in humin content. However, in the surface soil after the tillering stage, there is a significant increase in humic acid content, which is the main change in humic acid content. During the heading stage, the carbon content of humin in all treatments increased by more than 35%, with the most significant increase observed in the OF treatment. Surface soil humin acid is significantly influenced by cultivation methods after the tillering stage, showing OF > CF. Under conventional nitrogen application, the carbon content of humin acid in the OF treatment during the heading and maturity stages increased by 22.51% and 21.14%, respectively, compared to CF, and under the influence of N12, this increase was even higher, with significant differences observed. Additionally, in the surface soil after the tillering stage, compared to other treatments, OFN18 has a higher proportion of humic acid, reaching 39.11% during the heading stage and 37.38% during the maturity stage, indicating a higher conversion rate of organic carbon to humic acid in soil humus. Overall, as the growth process advances, the significant increase in humin content leads to a decrease in the proportion of humic acid. Compared to conventional cropping systems, organic farming significantly increases the humic acid content in the 0–20 cm soil layer, especially in the 0–10 cm soil layer. Among them, the OFN18 treatment is more conducive to the conversion of organic carbon to humic acid. Soil aggregates During the maturity stage, in all treatments, more than half of the soil aggregates are composed of macroaggregates with particle sizes larger than 2mm, with the remaining majority being microaggregates with particle sizes smaller than 0.106mm, accounting for 9–22% (Fig. 3 ). Macroaggregates with particle sizes larger than 2mm are predominantly influenced by cultivation methods, with a notable trend of OF > CF, particularly evident in the surface OF treatment. In the surface soil under N18, the content of macroaggregates larger than 2mm in OF is increased by 12.36% compared to CF, which decreases to 6.95% under N12, both showing significant differences. In the surface layer, the proportion of microaggregates with particle sizes between 0.106-0.25mm is higher in OF than in CF; however, in the subsoil layer, the trend is reversed, with CF > OF, and the differences are significant. In the surface layer, the proportion of microaggregates with particle sizes smaller than 0.106mm is influenced by cultivation methods, showing CF > OF; in the subsoil layer, influenced by nitrogen levels, it is N18 > N12. Among all treatments, OFN12 has the smallest proportion of microaggregates with particle sizes smaller than 0.106mm. In summary, soil aggregates of different particle sizes are influenced by different factors. However, in the 0-20cm soil layer, the proportion of macroaggregates larger than 2mm is higher in the OF treatment, with OFN12 treatment showing a higher proportion of macroaggregates larger than 0.25mm. Therefore, the structural integrity of water-stable aggregates, particularly under OFN12 treatment, is more rational, facilitating better regulation of soil aeration, water retention, nutrient preservation, and fertility release in field soils. Soil Enzyme Activity The effects of different cropping systems and nitrogen levels on three soil enzyme activities in the surface and subsurface soils at maturity are shown in Fig. 4 .Soil sucrase, a hydrolytic enzyme, catalyzes sucrose hydrolysis. In the mature stage of rice, surface soil sucrase activity is significantly higher than subsurface, especially under OF treatment. In surface soils, sucrase activity of CFN12 treatment lags. Under N12 levels, sucrase activity under OFN12 is higher than CF. Surface soil sucrase is affected by cultivation method and nitrogen application rate interaction. In subsurface soils, sucrase activity shows N12 > N18. Under CF and OF, N12 treatment has sucrase activity 40.62% and 55.93% higher than N18 treatment respectively. N18 inhibits sucrase in subsurface. OFN12 is more conducive to soil enzyme-catalyzed reactions. Soil cellulase activity reflects carbon cycle. Except for OFN12 treatment, subsurface has higher cellulase activity. In mature surface soils, OFN12 treatment has the highest cellulase activity, 32.71% higher than OFN18 treatment. In subsurface soils, cellulase activity is influenced by cultivation method and nitrogen level (OF > CF, N18 > N12). Only CFN12 treatment has significantly lower activity. OFN12 shows higher activity in both surface and subsurface. Soil leucine aminopeptidase activity helps assess nitrogen cycling. Surface has higher activity than subsurface. Across depths, CF > OF, with OFN12 > OFN18 > CFN18 > CFN12. Under OF treatment, leucine aminopeptidase activity is significantly higher than CF. Under N12, in 0–20cm soil layer, OF treatment enzyme activity is 34.47% and 49.95% higher than CF. Under N18, increase narrows. Under OF, N12 has 10.16% and 11.23% higher leucine aminopeptidase activity than N18 in 0–20cm soil layer. OFN12 > N18 under OF. Correlation analysis of soil indicators Taking mature soil samples as an example, Pearson algorithm was used to analyze the correlation among 15 physicochemical indicators including total nitrogen (TN), alkali-hydrolyzable nitrogen (AHN), ammonium nitrogen (NH 4 + -N), nitrate nitrogen (NO 3 − -N), total phosphorus (TP), available phosphorus (AP), organic matter (OM), pH, total carbon (TC), soil organic carbon (SOC), dissolved organic carbon (DOC), acid extractable organic carbon (AOC), sucrase (SUC), leucine aminopeptidase (LAP), and cellulase (CEL). The results are shown in Fig. 5. Overall, in the surface soil, except for pH, mineral nitrogen content influenced by pH, and slightly lower total phosphorus content, all other fertility, carbon, nitrogen, and enzyme activity indicators showed significant or extremely significant positive correlations. Particularly, the positive correlation was more pronounced in the soil carbon pool-related indicators. In this study, compared to the subsoil, the relationship between fertility indicators, active carbon and nitrogen indicators, and enzyme activity is closer in the surface soil, and their mutual promotion effect is more significant. Figure 5. Correlation analysis of soil nutrients, enzyme activity, and active carbon and nitrogen in soil (A) 0–10 cm;(B) 10–20 cm Principal component analysis of soil indicators Taking mature soil samples as an example, principal component analysis was conducted on the 21 physicochemical indicators including TN, AHN, NH4+-N, NO3–N, TP, AP, OM, pH, TC, SOC, DOC, AOC, SUC, LAP, CEL, fulvic acid (FA), humic acid (HA), humin (HM), proportion of different aggregate sizes (> 2 mm, 0.25-2 mm, < 0.25 mm). The results are shown in Fig. 6 , where the cumulative variance contribution rates of the major components PC1 and PC2 reached 72.4% and 64.6% in the surface and subsoil, respectively, explaining the differences among the four treatments well. Scores on PC1 and PC2 were calculated for each treatment to represent soil properties comprehensively. The ranking of treatments in the 0-10cm soil depth was(Table 4 ): OFN12 > OFN18 > CFN18 > CFN12; and in the 10-20cm depth, it was OFN12 > OFN18 > CFN12 > CFN18. The scores showed that OF > CF in both soil depths, with N18 < N12. As shown in Fig. 6 (a), in the surface soil, the active carbon index had positive effects on enzyme activity, organic matter content, some active nitrogen indices, and the proportion of aggregate sizes > 0.25 mm to varying degrees. The input of organic materials significantly improved some soil fertility indicators and the active carbon index while reducing the proportion of aggregate sizes < 0.25 mm. Notably, when moderate organic fertilizer was applied, organic matter, enzyme activity, and the proportion of 0.25-2 mm aggregates increased significantly. Enzymatic reactions were enhanced in a more suitable organic matter environment for microbial growth, with excellent enzyme activity in OFN12. Excessive organic fertilizer input led to an increase in the active nitrogen index and the proportion of aggregates > 2mm, favoring humic acid derivatives. In the subsoil (Fig. 6 (b)), the overall advantage of soil indicators in OFN12 was slightly lower than in the surface soil. The impact of organic materials on soil organic matter content, active carbon and nitrogen indices, enzyme activity, humic acid proportion, and large aggregates in the subsoil was not as significant as in the surface soil, depending on the input amount. In conclusion, compared to conventional cultivation, organic cultivation improved soil properties and facilitated soil improvement while promoting cultivation. OFN12 showed a significant improvement in specific soil indicators such as enzyme activity and carbon pool indices, while OFN18, although less pronounced in increasing soil indicators than OFN12, had a more comprehensive promotion effect on multiple indicators. Specifically, in the surface soil, the synergistic effect of organic cultivation and reduced nitrogen fertilization yielded the best improvement results. Table 4 Integrated scores of soil indicators for different treatments Soil layer Treatment PC1 PC2 Total points Rank 0–10 cm CFN12 -3.5306 -0.50979 -4.04039 4 CFN18 -2.44123 0.709985 -1.73125 3 OFN12 3.149705 2.59166 5.741365 1 OFN18 2.82213 -2.79186 0.03027 2 10–20 cm CFN12 -4.27673 1.25186 -3.02487 3 CFN18 0.0382 -3.49288 -3.45468 4 OFN12 2.494955 2.32264 4.817595 1 OFN18 1.743565 -0.08163 1.66194 2 Discussion Influence of organic cultivation and reduced nitrogen fertilization on soil carbon and nitrogen pools Although the response mechanisms of various soil organic carbon fractions to fertilization measures may vary, previous studies have shown that overall, heavy use of chemical fertilizers and biased nitrogen application may inhibit soil organic carbon and active organic carbon content 28 , 29 . In this experiment, the surface soil organic carbon content under the CFN18 treatment was higher before the maturity period, while the OFN12 treatment could maintain soil organic carbon content at a higher level across all three periods, indicating overall higher soil fertility under this treatment. This may be attributed to the low carbon-to-nitrogen ratio in the soil due to nitrogen fertilizer application, promoting organic matter decomposition 30 . As the experimental plots were paddy fields in the early to mid-growth periods of rice, compared to upland areas, the soil organic matter has less contact with the external environment, and the anaerobic nature of organic carbon in the soil makes the carbon-to-nitrogen ratio and organic carbon content more stable. Therefore, the CFN18 treatment could maintain a good organic carbon content before the maturity period, but during the field drying at maturity, a large amount of organic carbon began to decompose upon contact with air, consistent with previous research findings. As one of the active components of soil carbon pools 31 , soluble organic carbon, due to its dissolution characteristics under certain conditions, can rapidly move in soil and water bodies 32 , facilitating microbial mineralization and crop root absorption 33 . Soluble organic carbon includes water-soluble organic carbon, organic acids, humic acids, and other complex components primarily provided by plant residues, organic materials, and soil humus 34 . This study found that except for the subsoil, the soluble organic carbon content under organic cultivation was significantly higher than conventional cultivation, indicating that organic cultivation could provide a large amount of highly efficient and easily absorbable active organic carbon components for plants. However, by the time of field drying at maturity, the soluble organic carbon in the subsoil was significantly depleted. This suggests that organic cultivation, organic fertilization, cultivation practices, and soil physical properties may directly enhance the content of active organic carbon sensitive to external changes. Acid-extractable organic carbon represents the content of proteins 35 , polysaccharides, and ribose in the soil through partial hydrolysis by hot concentrated hydrochloric acid(Xu et al., 1997). Proteins mainly originate from soil organic matter and can be degraded by microorganisms to form amino acids 37 ; polysaccharides provide energy for soil organisms and crops, promoting microbial reproduction and enhancing microbial metabolic activity and organic matter production, thus improving soil fertility 38 . High protein and polysaccharide content form a beneficial cycle, where rich organic matter provides a good living environment for microorganisms 39 , reducing their competition with roots for nutrients. Compared to conventional cultivation, the results of this experiment show that organic cultivation significantly increased the content of acid-extractable organic carbon, indicating that organic fertilizers increased soil organic matter content, promoted soil microbial metabolism, and increased protein and polysaccharide content. These results demonstrate that organic cultivation can effectively enhance soil organic carbon content and active organic carbon content, helping to improve soil fertility and microbial activity levels. Influence of organic cultivation and reduced nitrogen fertilization on soil aggregates and humus One of the signs of soil degradation under continuous cropping is the loss of soil organic matter and a decrease in aggregate size, indicating that aggregates can characterize soil fertility 40 . In this experiment, the proportion of large aggregates with a size greater than 2 mm in both soil layers was significantly influenced by the cultivation method, showing organic > conventional. Under organic cultivation, the proportion of large aggregates with a size greater than 0.25 mm was higher, with the highest increase in the proportion of aggregates with a size of 0.5-1 mm in the N12 treatment. The improvement effect of organic cultivation on soil aggregates observed in the experiment is consistent with previous findings 41 . As the main component of organic matter in aggregates, the formation and transformation of humus are crucial for maintaining the stability of aggregates 42 . Humus is involved in the formation of aggregates, promoting soil carbon storage function and enhancing carbon sequestration capacity 43 . Typically, compost can enhance soil fertility because the humus formed during composting effectively supplements the humus deficit caused by soil fertility consumption 44 . Humic acid is a major component of humus, and different components of humic substances have varying effects on aggregate formation: the content of humic acid in humic substances is a key factor affecting aggregate stability, while the influence of fulvic acid is relatively minor 45 . Research has shown that after adding different concentrations of humic acid to soil, the content of water-stable aggregates in soils with different degrees of erosion will increase 46 . In this experiment, there was no significant change in the fulvic acid content in the soil after the tillering stage, with limited impact on soil aggregates. Under organic cultivation conditions, the humic acid content in the soil at 0–10 cm depth significantly increased, leading to a higher proportion of large aggregates with a size greater than 2 mm and greater than 0.25 mm at maturity. Organic cultivation has a positive effect on increasing humic acid content and promoting the process of aggregate formation, significantly increasing the proportion of large aggregates, especially evident in the OFN12 treatment at maturity. The impact of different nitrogen fertilizer levels on aggregates and humus was relatively small, but a reasonable nitrogen fertilizer level combined with organic cultivation can have a positive effect on the structure of aggregates and humus composition. In summary, organic cultivation significantly increases the humic acid content and the proportion of humic acid, improving the structure of soil aggregates, promoting soil carbon storage, and avoiding the decrease in aggregate size and soil loss issues after repeated tillage. Impact of organic cultivation and reduced nitrogen fertilization on soil enzyme activity This study demonstrated that organic cultivation significantly increased the activity of sucrase, leucine aminopeptidase, and cellulase in the soil, especially in the mature stage of the surface soil. This increase may be related to the use of the previous crop, milk vetch, in the experiment. The decomposition of milk vetch provided abundant organic matter and a suitable microenvironment, promoting microbial reproduction and activity in the soil, thereby enhancing soil microbial activity and enzyme activity. This is consistent with previous research findings that green manure can increase the activity of enzymes involved in nitrogen cycling 47 . Additionally, the reduced nitrogen fertilization measures adopted in organic cultivation also showed positive effects, especially in increasing the activity of leucine aminopeptidase in the soil. This improvement may be related to the imbalance in microbial community structure caused by the reduction of excess nitrogen 48 . In conclusion, organic cultivation and reduced nitrogen fertilization measures have a significant impact on the enhancement of soil enzyme activity, providing favorable conditions for the growth and activity of soil microbial communities, thereby contributing to maintaining soil health and biological activity. Conclusion Organic cultivation combined with moderate nitrogen reduction treatments increased the TOC, SOC, DOC, AOC, and AHN content across different stages. Soil enzyme activities in the plough layer were significantly influenced by the cultivation method, with organic cultivation surpassing conventional methods. Organic cultivation notably enhanced humic acid content in the 0–10 cm soil layer compared to conventional cultivation. This increase in humic acid content promoted the aggregation of macroaggregates in the plough layer. Comprehensive soil fertility assessments indicated that organic treatments outperformed conventional treatments, and appropriate nitrogen reduction fertilization were superior to conventional nitrogen applications. These findings illuminate a promising avenue for sustainable agricultural solutions, underscoring closer associations and superior integrated effects among soil carbon and nitrogen pools, enzyme activities, and nutrient contents under organic cultivation combined with appropriate nitrogen reduction fertilization. Continued research into these cultivation patterns combined with varying nitrogen application rates holds promise for improving cultivated land quality and promoting sustainable rice cultivation, paving the way for optimal nitrogen application rates and cultivation methods to enhance soil fertility sustainably and achieve high rice yields. Declarations Competing interests The authors have no relevant financial or non-financial interests to disclose. Author Contribution G.W.: Writing – original draft, Data curation, Formal analysis,Resources. Y.C.: Conceptualization, Data curation, Methodology. Y.C.: Writing – review & editing. X.H.: Data curation, Resources. S.Y.: Data curation, Resources. M.J.: Writing – review & editing. Z.Z.: Funding acquisition, Methodology, Supervision. L.H.: Project administration, Funding acquisition Supervision, Validation, Writing – review & editing. All authors reviewed the manuscript. Acknowledgement This work was supported by Special Funds for Scientific and Technological Innovation of Jiangsu province, China (BK20220017) and Jiangsu Province Postgraduate Research Innovation Program (KYCX24-3785).We thank all the colleagues of Yangzhou Mabangwan Ecological Agricultural Science and Technology Co. for their help during the experimental field. Data Availability All data generated or analysed during this study are included in this published article. References Khan, Z., Zhang, K., Khan, M. N., Zhu, K. & Hu, L. Effects of biochar persistence on soil physiochemical properties, enzymatic activities, nutrient utilization, and crop yield in a three-year rice-rapeseed crop rotation. Eur. J. Agron. 154 , 127096 (2024). 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Wang, Y. et al. Intercropping-driven nitrogen trade-off enhances maize productivity in a long-term experiment. Field Crops Res. 287 , 108671 (2022). Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5163192","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":376471885,"identity":"d12df21e-771a-4cae-9dd0-a6d206edb6d2","order_by":0,"name":"Guanghua Wang","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"prefix":"","firstName":"Guanghua","middleName":"","lastName":"Wang","suffix":""},{"id":376471886,"identity":"be946042-8fef-4af2-9b3f-1db38692a3b5","order_by":1,"name":"Yuanjie Chen","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"prefix":"","firstName":"Yuanjie","middleName":"","lastName":"Chen","suffix":""},{"id":376471888,"identity":"ee37ca9c-4472-4f5f-ac94-2fa5b6f66bdd","order_by":2,"name":"Yuqi Chen","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"prefix":"","firstName":"Yuqi","middleName":"","lastName":"Chen","suffix":""},{"id":376471889,"identity":"10e097c6-1174-4cc8-9afc-6b607bb499a8","order_by":3,"name":"Shilong Yu","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"prefix":"","firstName":"Shilong","middleName":"","lastName":"Yu","suffix":""},{"id":376471890,"identity":"91bdc3c3-4361-490f-9e24-9069d07839d8","order_by":4,"name":"Xiaomin Huang","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"prefix":"","firstName":"Xiaomin","middleName":"","lastName":"Huang","suffix":""},{"id":376471891,"identity":"93405d9b-e47e-4fba-b60b-4af5d300e5c1","order_by":5,"name":"Min Jiang","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"prefix":"","firstName":"Min","middleName":"","lastName":"Jiang","suffix":""},{"id":376471892,"identity":"9348f162-d867-4d8e-94f5-d8227cf0b838","order_by":6,"name":"Zujian Zhang","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"prefix":"","firstName":"Zujian","middleName":"","lastName":"Zhang","suffix":""},{"id":376471893,"identity":"226037b5-20e0-4b3f-b400-793efadb51fc","order_by":7,"name":"Lifen Huang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0ElEQVRIiWNgGAWjYBACPuYzYFoOwmUjQgsbWw6YNiZdS2IDCVp4j0n83FGbvuH8GQOGD2WHGfhnNxDSwpcm2XvmeO6GA2cMGGecO8wgcecAAS3yPWYSvG3Hcjcc7DFg5m07zGAgkUDIFh4zyb9tx9INDvMYMP8lVos0b1tNgsExoBZGIrUYW8u2HTCceYat4GDPuXQeiRsEtPCz8RjefNtWJ893/vDGBz/KrOX4ZxDQAgWHGRQOMDAAEQMPUeqBoI5BvoFYtaNgFIyCUTDiAACngD2eyjgK9AAAAABJRU5ErkJggg==","orcid":"","institution":"Yangzhou University","correspondingAuthor":true,"prefix":"","firstName":"Lifen","middleName":"","lastName":"Huang","suffix":""}],"badges":[],"createdAt":"2024-09-27 07:38:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5163192/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5163192/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":69935023,"identity":"29781360-e038-4013-a48d-9a4e35ead043","added_by":"auto","created_at":"2024-11-26 18:46:19","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":2290069,"visible":true,"origin":"","legend":"\u003cp\u003eSoil organic carbon content under organic and conventional cultivation at two nitrogen levels CFN12: Conventional cultivation low nitrogen treatment, CFN18: Conventional cultivation high nitrogen treatment, OFN12: Organic cultivation low nitrogen treatment, OFN18: Organic cultivation high nitrogen treatment. Different lower case letters indicate significant differences among the four treatments at p\u0026lt;0.05.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5163192/v1/959b8328047878c13fa07ef8.jpeg"},{"id":69935026,"identity":"19b2de80-f46d-4412-ba40-4938a66432b6","added_by":"auto","created_at":"2024-11-26 18:46:19","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":3333975,"visible":true,"origin":"","legend":"\u003cp\u003eSoil humus organic carbon content under organic and conventional cultivation at two nitrogen levels CFN12: Conventional cultivation low nitrogen treatment, CFN18: Conventional cultivation high nitrogen treatment, OFN12: Organic cultivation low nitrogen treatment, OFN18: Organic cultivation high nitrogen treatment. Different lower case letters indicate significant differences among the four treatments at p\u0026lt;0.05.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5163192/v1/369f3098b12ac1fc51300250.jpeg"},{"id":69935021,"identity":"57db9cd7-80e7-4f93-8da1-98201583da35","added_by":"auto","created_at":"2024-11-26 18:46:18","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":3254758,"visible":true,"origin":"","legend":"\u003cp\u003ePercentage of soil aggregates under organic and conventional cultivation at two nitrogen levels Different lower case letters indicate significant differences among the four treatments at p\u0026lt;0.05.\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5163192/v1/937680a7e5302650f9dec70d.jpeg"},{"id":69935024,"identity":"8452e845-024c-4308-818e-190b2cb71c3d","added_by":"auto","created_at":"2024-11-26 18:46:19","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":3404115,"visible":true,"origin":"","legend":"\u003cp\u003eConcentrations of three enzymes under organic and conventional cultivation at two nitrogen levels F, Cultivation Pattern; N, Nitrogen Level; F×N, interaction between F and N. Different lower case letters indicate significant differences among the four treatments at p\u0026lt;0.05.\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5163192/v1/dc2f297e74df14f18b6f68d8.jpeg"},{"id":69935022,"identity":"b95761c6-bb4d-4f4a-98d4-14fa2719a9c1","added_by":"auto","created_at":"2024-11-26 18:46:19","extension":"jpeg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1221814,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation analysis of soil nutrients, enzyme activity, and active carbon and nitrogen in soil\u003cstrong\u003e \u003c/strong\u003e(A) 0-10 cm；(B) 10-20 cm\u003c/p\u003e","description":"","filename":"floatimage5.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5163192/v1/272052cc905420f482e77bc6.jpeg"},{"id":69935027,"identity":"0310a7be-2a82-4258-bac3-7373a94ac8ea","added_by":"auto","created_at":"2024-11-26 18:46:19","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":6175551,"visible":true,"origin":"","legend":"\u003cp\u003ePrincipal component analysis of soil nutrients, enzyme activity, and active carbon and nitrogen in soil (a) 0-10 cm；(b) 10-20 cm\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-5163192/v1/b6990be93a5a66d1535daf72.jpeg"},{"id":72137817,"identity":"1d418aed-ce7a-4b4b-8f16-6d30d9fb6aba","added_by":"auto","created_at":"2024-12-23 06:03:05","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":20655327,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5163192/v1/feb48474-932d-4968-9f2c-362638115fd6.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Optimizing effects of organic farming and moderately low nitrogen levels on soil carbon and nitrogen pools, humus composition and related enzyme activities","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe physicochemical properties of soil serve as crucial indicators for assessing soil health and productivity, exerting significant influences on crop growth, environmental quality, and climate change \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. In recent years, with the development of intensive agriculture, improper cultivation practices have significantly impacted the physicochemical properties of soil. Organic cultivation and moderate reduction in nitrogen fertilization can effectively improve soil physicochemical properties, gradually ameliorating soil conditions without compromising crop yields \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e, aligning with the future trend of sustainable agriculture.\u003c/p\u003e \u003cp\u003eSoil nitrogen pool represents the total amount of nitrogen stored in the soil. Nitrogen fertilization management practices have a significant impact on soil nitrogen pool. Due to limitations in traditional agriculture, excessive application of chemical or nitrogen fertilizers, compared to organic fertilizers, leads to a significant decrease in soil carbon-nitrogen ratio, which has become a consensus in recent years. Moderately reducing nitrogen fertilizer application can prevent land degradation, yield reduction due to nitrogen deficiency, or decreased fertilizer efficiency and environmental harm caused by excessive nitrogen fertilization. Adequate nitrogen fertilization can enhance soil nitrogen supply capacity to meet crop nitrogen demand. However, excessive nitrogen application can lead to nitrogen leaching, causing environmental pollution. Yang et al. \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e also found that organic cultivation can increase soil nitrogen supply capacity while reducing nitrogen leaching, providing theoretical support for the combination of organic cultivation and moderate reduction in nitrogen fertilizer application.\u003c/p\u003e \u003cp\u003eSoil carbon pool refers to the total amount of organic carbon stored in the soil, which has a significant impact on global carbon balance. Even slight changes in soil carbon pool can have important effects on global carbon balance. Organic cultivation can increase soil carbon storage by increasing organic matter input into the soil. Compared with conventional cultivation, organic cultivation can increase soil organic matter content by 20\u0026ndash;50%\u003csup\u003e4\u003c/sup\u003e. Increasing soil carbon storage can improve soil fertility, enhance soil structure, and mitigate climate change through carbon sequestration\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Current research has found that most nitrogen and organic carbon in soil aggregate in water-stable macroaggregates with particle sizes of 0.25-2 mm. Reasonable nitrogen addition can promote the formation of these aggregates, while enhancing organic carbon content within them\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Additionally, Thomaz et al. \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003efound that 100\u0026thinsp;~\u0026thinsp;200 \u0026micro;m microaggregates are formed by the adsorption of soil microorganisms on organic residues, providing evidence for the promotion of aggregate formation by organic cultivation. Microaggregates larger than 0.05 mm have advantages in adsorbing humic acid due to their larger contact area with the external environment, promoting mineralization reactions between microorganisms and humic acid\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. Humic acid's moderate binding characteristics enable it to form good aggregate structures with soil particles or sand particles. The proportion of humic acid to fulvic acid can effectively evaluate the quality of soil humus, serving as an important indicator for maintaining or improving soil fertility, and it is an essential component of soil nutrients\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. Organic materials can promote the formation of soil humus, mainly by increasing the proportion and activity of humic acid in humic acid\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Humic acid in humus is usually considered inert matter in soil and mainly participates in the soil organic carbon cycle\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e, serving as a carbon source. During the formation of humus, mineralization of organic nitrogen and denitrification of nitrate nitrogen may lead to the production of gases such as ammonia, nitrogen, and nitrogen dioxide, affecting the process of nitrogen fixation in soil\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. Therefore, selecting organic materials rationally is crucial to promote humus formation while controlling nitrogen volatilization reactions. The composition of soil humus is significantly influenced by natural conditions and human management activities, and studying these changes helps understand the effects of different nitrogen application rates on soil carbon cycling\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eQ. Wang et al. \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003efound that long-term excessive application of chemical fertilizers can lead to a decrease in organic carbon and humus content, exacerbating soil acidification. The combined application of chemical and organic fertilizers not only contributes to the accumulation of organic carbon and humus but also promotes the humification process of soil, improving the soil microecological environment. Numerous studies have explored the effects of returning organic materials to soil on the form and content of soil humus, but these effects are greatly influenced by soil type, climate conditions, and the amount of exogenous organic material input. In addition, different plant root exudates and residues have varying degrees of impact on soil microbial community metabolic activities and humus forms\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Soil enzyme activity often represents the intensity of soil microbial activity. Adopting organic cultivation measures and moderate nitrogen fertilization can promote soil microbial activity and increase the activity of various soil enzymes\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Among them, leucine aminopeptidase is closely related to soil nitrogen cycling\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e, and soil sucrase catalyzes the hydrolysis of sucrose in soil into monosaccharides more conducive to rhizosphere absorption\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e. By measuring the changes in the activity of these specific enzymes, the transformation rate of relevant products in the soil and the rate of nutrient synthesis can be indirectly inferred.\u003c/p\u003e \u003cp\u003eThis study focuses on organic cultivation and nitrogen application levels to systematically analyze their effects on soil physicochemical properties by investigating soil carbon storage, nitrogen supply, humus composition, and enzyme activity indicators. Previous studies have focused on nitrogen fertilizer management and cultivation methods, without in-depth research on changes in soil aggregates and humus composition. Therefore, this study is expected to provide theoretical support for the combination of nitrogen reduction fertilization and organic cultivation in planting models by examining soil physicochemical properties.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eExperimental design\u003c/h2\u003e \u003cp\u003eThe experimental field was located within the Ma Peng Wan Ecological Agriculture Co., Ltd. in Gaoyou City, Yangzhou, Jiangsu Province, China, from 2021 to 2022 (longitude 119\u0026deg;25', latitude 32\u0026deg;47'), situated in the northern subtropical monsoon humid climate zone of China. The average annual temperature is approximately 16.2\u0026deg;C, with an annual precipitation of about 1341.5 mm and an annual sunshine duration of around 2100 hours. The frost-free period lasts approximately 221 days. The company is located in Tayuan Village, Mapeng Town, Gaoyou City, covering an area of 135 ha. In 2011, the China Organic Food Certification Center (COFCC) granted it the organic food conversion certification and it is a modern ecological organic farm specializing in the cultivation of organic rice. The experimental field has been dedicated to organic cultivation research since 2012, with stable soil properties characterized by clay loam texture. The soil property is stable and the texture is clay loam. The soil sample collected in June 2022 contained 27.93 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e organic matter, 112.24 mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e alkali-hydrolyzable nitrogen, 7.36 mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e available phosphorus, 61.08 mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e available potassium, and 1.31 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e total nitrogen. The pH of the sample was 8.13.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eTest materials\u003c/h3\u003e\n\u003cp\u003eThis experiment utilized high-yield rice varieties commonly grown in the middle and lower reaches of the Yangtze River, namely Nanjing 46 (Nanjing46, \u003cem\u003eJaponica\u003c/em\u003e), with a full growth period of 165 days, and Huai Fragrant Jing 15 (Huaixiangjing15, \u003cem\u003eJaponica\u003c/em\u003e), with a full growth period of 150 days.\u003c/p\u003e \u003cp\u003eTillage practices\u003c/p\u003e \u003cp\u003eThe experimental plots were designed using a split-plot design, with planting methods (organic planting, conventional planting) as the main plots and nitrogen input levels during the rice season (180, 270 kg/hm\u0026sup2;) as the subplots, with an area of 49 m\u0026sup2; (7 m \u0026times; 7 m) each, replicated three times. Purple clouds were planted as the previous crop, and the test rice was sown on May 18, 2022, with manual transplanting on June 9, using a spacing of 0.3 m \u0026times; 0.125 m, with 3 seedlings per hill. The main plots of planting methods were distributed in adjacent fields with similar fertility, separated by ridges, and isolated between subplots with small ridges, covered with plastic film to ensure separate irrigation and drainage for each subplot.\u003c/p\u003e \u003cp\u003eConventional cultivation (CF) followed local practices for high-yield cultivation management in Gaoyou, with 45% compound fertilizer (containing 15% nitrogen) applied as base fertilizer one day before rice transplanting. Urea was applied as topdressing fertilizer in three installments: first tillering, second tillering, and heading. Management measures for disease, pests, and weeds were implemented according to conventional cultivation requirements. Organic cultivation (OF) was managed according to the national standards for organic product production (GB/T19630.1), adopting the milk vetch-rice planting pattern. Milk vetch (containing 0.33% nitrogen) were plowed and applied as base fertilizer two weeks before rice transplanting. Rapeseed cake (containing 4.60% nitrogen) and bio-organic fertilizer (containing 4.00% nitrogen) were applied as base fertilizer one day before rice transplanting, with bio-organic fertilizer applied as topdressing fertilizer in mid-July as heading fertilizer. N18 equivalent to pure nitrogen 270 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (conventional nitrogen application by local farmers) and N12 equivalent to pure nitrogen 180 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (nitrogen reduction treatment in the experiment). Specific fertilization strategies are shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Organic rice production throughout the process complies with organic rice production management regulations, with disease and pest control exclusively using certified organic pesticides, and manual weeding in the plots.\u003c/p\u003e \u003cp\u003eAfter two years of the above-mentioned cultivation and fertilization management positioning, the experimental plots focused on soil research in 2022.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFertilization rate under organic and conventional cultivation nitrogen levels (kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"11\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eCultivate\u003c/p\u003e \u003cp\u003eWay\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eNitrogen application level\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTotal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"4\" nameend=\"c8\" namest=\"c5\"\u003e \u003cp\u003eBasal fertilizer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e \u003cp\u003eTopdressing fertilizer\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCompound fertilizer(15%N)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eMilk vetch(0.33%N)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eRapeseed cake(4.6%N)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eBio-organic fertilizer(4%N)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eUrea(46%N)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eBio-organic fertilizer(4%N)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eCF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e229\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e270\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e750\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e343\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eOF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e12000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e1200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e930\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e270\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e12000\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2400\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e/\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e1800\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe nutrient contents of various fertilizers are: compound fertilizer: 15%N, 15% P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and 15% K\u003csub\u003e2\u003c/sub\u003eO; Milk vetch: 0.33% N, 0.08% P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e and 0.23% K\u003csub\u003e2\u003c/sub\u003eO; Rapeseed cake: 4.60% N, 0.80% P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, 1.04% K\u003csub\u003e2\u003c/sub\u003eO, 0.80% Ca, 0.48% Mg and various trace elements; Bio-organic fertilizer: 4.00% N, 1.87% P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e, 2.28% K\u003csub\u003e2\u003c/sub\u003eO, Various organic acids, peptides and rich nutrient elements including 53% organic matter.\u003c/p\u003e\n\u003ch3\u003eSoil sample collection\u003c/h3\u003e\n\u003cp\u003eSoil samples were collected using a soil sampler at the tillering stage, heading stage, and maturity stage of rice growth, following a five-point sampling method. Soil samples were taken from depths of 0\u0026ndash;10 cm (surface layer) and 10\u0026ndash;20 cm (subsurface layer) in each plot. After uniformly mixing the soil samples from each plot, plant roots and stones were removed, and a portion of the samples was stored in sealed bags and placed in a -70\u0026deg;C freezer as fresh samples for subsequent determination of soil active carbon and nitrogen. The remaining soil samples were air-dried completely and sieved through a 100-mesh sieve for further analysis. Additionally, at the maturity stage, soil aggregates were collected in the field using a shovel (with the premise of not disturbing the original soil structure) for aggregate determination.\u003c/p\u003e\n\u003ch3\u003eDetermination of soil nutrient content\u003c/h3\u003e\n\u003cp\u003eSoil total nitrogen was determined using the semi-micro Kjeldahl method, soil organic matter was determined using the potassium dichromate heating external heating method, and soil alkali-hydrolyzable nitrogen was determined using the alkali diffusion method\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003eDetermination of soil enzyme activity\u003c/h3\u003e\n\u003cp\u003eFor air-dried soil samples at the maturity stage of rice, soil sucrase, soil cellulase, and soil leucine aminopeptidase activities were determined separately. Soil sucrase activity was determined using the 3,5-dinitrosalicylic acid colorimetric method\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e, with enzyme activity expressed as the amount of glucose produced per gram of soil after 1 day; soil cellulase activity was determined using the anthrone colorimetric method\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e, with enzyme activity expressed as the amount of glucose produced per gram of soil after 1 day; soil leucine aminopeptidase activity was determined using the p-nitroaniline colorimetric method \u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e, with enzyme activity expressed as the amount of p-nitroaniline produced per gram of soil after 1 day.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eDetermination of soil active carbon and nitrogen indices\u003c/h2\u003e \u003cp\u003eFor air-dried soil samples at the tillering stage, heading stage, and maturity stage of rice, soil organic carbon was determined using the low-temperature external heating potassium dichromate oxidation-colorimetric method\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e. The TOC-L CPH total organic carbon analyzer was used to determine soil total carbon, inorganic carbon, and soluble organic carbon in air-dried soil samples at the tillering stage, heading stage, and maturity stage of rice\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Ammonium nitrogen and nitrate nitrogen were determined using a continuous flow analyzer (Proxima) after extraction with 1 mol\u0026middot;L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e KCl solution from air-dried soil samples at the tillering stage, heading stage, and maturity stage of rice. Acid hydrolysis method was used to determine acid hydrolyzable organic carbon according to the method of Rovira and Vallejo \u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eDetermination of soil aggregates\u003c/h3\u003e\n\u003cp\u003eThe wet sieving method \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e was used to determine water-stable aggregates. Samples were taken at the maturity stage, and fresh soil was retrieved from the field using a shovel (with the premise of not disturbing the original soil structure). Soil samples were split along the soil sample gaps, removing residual broken stems, roots, stones, and other impurities. The samples were turned every 3\u0026ndash;4 hours, and the soil samples were continuously split along the gaps until the soil samples could be directly crushed by hand rather than flattened when pinched. The soil samples were processed in this manner and air-dried to a moisture content slightly below 10% for analysis. Initially, 10 g of soil sample was dried to a constant weight to calculate the moisture content. Subsequently, 50 g of soil sample was placed in a vibrating mechanical sieve shaker, subjected to vertical oscillation with an amplitude of 3 cm and a duration of 30 minutes for wet sieving. The soil samples separated in five sieves (2 mm, 1 mm, 500 \u0026micro;m, 250 \u0026micro;m, 106 \u0026micro;m) were transferred and dried at 50\u0026deg;C. The proportion of aggregates of different particle sizes in the soil was calculated based on the moisture content and the dry weight of the soil samples in different sieves.\u003c/p\u003e\n\u003ch3\u003eDetermination of soil humus content\u003c/h3\u003e\n\u003cp\u003eSoil humus content was determined using the modified humus composition method\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e on air-dried soil samples collected at the maturity stage of rice.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eData analysis methods\u003c/h2\u003e \u003cp\u003eMicrosoft Excel 2021 and SPSS 23.0 software were used for data organization and analysis, with Origin 2022 used for graphical representation. Data from each treatment (cultivation method and nitrogen level combination) were subjected to one-way analysis of variance (ANOVA), and LSD (Least Significant Difference) was used to compare differences in the data.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eSoil organic carbon\u003c/h2\u003e \u003cp\u003eThe organic carbon content of soil surface and subsurface under different planting systems and nitrogen levels at three sampling stages is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Overall, soil organic carbon is influenced by the interaction between cultivation methods and nitrogen levels, with significantly higher levels in the soil surface compared to the subsurface. During the tillering and heading stages, the organic carbon content in the soil surface is significantly higher under certain cultivation methods and nitrogen levels, with CFN18 and OFN12 exhibiting the highest organic carbon content. In the subsurface, there is no significant pattern, and differences between treatments are minimal. During the tillering stage, the organic carbon content in the soil surface is significantly higher in OFN12 compared to CFN12, and in CFN18 compared to OFN18; however, these differences diminish during the heading stage, with increases of 7.42% and 8.12%, respectively. During the maturity stage, the organic carbon content in the soil surface is significantly higher in OFN12 treatment compared to other treatments.\u003c/p\u003e \u003cp\u003eThese results indicate that CFN18 or OFN12 treatments can increase the organic carbon content in the soil surface during the tillering stage, with the increase from CFN18 treatment gradually diminishing as the growth progresses, disappearing by the maturity stage. The organic carbon content in the subsurface soil is minimally affected by treatments. OFN12 treatment consistently results in higher organic carbon content in both soil layers and across all stages, promoting rice growth.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eSoil Carbon Pool\u003c/h2\u003e \u003cp\u003eThe content and variance analysis of soil total carbon components under two nitrogen levels in organic and conventional cultivation at three sampling periods are presented in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Overall, the total carbon content at different periods is higher in the soil surface compared to the subsurface. Differences between treatments are primarily observed in the surface soil during the tillering stage and the subsurface soil during the maturity stage, with no significant differences during the heading stage. During the tillering stage, the total carbon content in the surface soil is mainly influenced by the interaction between cultivation methods and nitrogen levels. Specifically, the total carbon content in CFN18 treatment is 41.07% higher than that in OFN18 treatment, and 22.51% higher in OFN12 treatment compared to CFN12 treatment, with both differences being significant. In the surface soil during the maturity stage, total carbon is influenced by cultivation methods, with OFN\u0026thinsp;\u0026gt;\u0026thinsp;CF, and differences between treatments are not significant. In the subsurface soil during the maturity stage, total carbon is significantly influenced by the interaction between cultivation methods and nitrogen levels, showing a pattern opposite to that of the surface soil during the tillering stage, with higher total carbon content observed in CFN12 and OFN18 treatments compared to other treatments. In summary, OFN12 treatment can increase the total carbon content in the surface soil during all three periods, while CFN12 and OFN18 treatments increase the total carbon content in the subsurface soil.\u003c/p\u003e \u003cp\u003eOverall, the soluble organic carbon content in the soil surface was significantly higher than that in the subsurface during all three periods, with the largest difference observed during the maturity stage. In the OF treatment during the maturity stage, the difference in soluble organic carbon content between different soil layers was the greatest (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The pattern of soil soluble organic carbon was highly consistent across all three periods, with OF\u0026thinsp;\u0026gt;\u0026thinsp;CF observed except in the subsurface during the maturity stage. Taking the surface soil during the maturity stage as an example, under N12, the OF treatment increased the soluble organic carbon content by 37.22% compared to CF treatment; under N18, this increase was 42.89%, both significant. Additionally, in the surface soil under the OF treatment, the soluble organic carbon content was higher under N18 than N12, with a difference of 12.41% during the maturity stage, which was significant. These findings indicate that OF significantly increases soil soluble organic carbon content, with the greatest increase observed in the surface soil during the maturity stage. In organic cultivation, the effect of increasing soluble organic carbon content is better under N18 compared to N12, particularly evident during the maturity stage.\u003c/p\u003e \u003cp\u003eThe organic carbon content in the surface soil was higher than that in the subsurface. Differences among treatments were mainly observed in the surface soil during all periods (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The content of acid hydrolysis organic carbon in the surface soil gradually increased after the tillering stage; after the heading stage, there was still a slight increase in the OF treatment, while a decrease was observed in the CF treatment. After the heading stage, there were no significant differences in the content of acid hydrolysis organic carbon among treatments in the subsurface soil. Across all three periods, the content of acid hydrolysis organic carbon in both soil layers was significantly influenced by cultivation methods, showing OF\u0026thinsp;\u0026gt;\u0026thinsp;CF, with significant differences. Additionally, influenced by nitrogen levels, it exhibited N18\u0026thinsp;\u0026gt;\u0026thinsp;N12. During the maturity stage, the difference in acid hydrolysis organic carbon content in the surface soil under different cultivation methods was the greatest. Under N18, the OF treatment increased the content of acid hydrolysis organic carbon by 41.02% compared to CF, and under N12, this increase was also 38.71%. In summary, OF significantly increases the content of soil acid hydrolysis organic carbon, particularly evident in the surface soil during the maturity stage. Additionally, N18 promotes the increase in acid hydrolysis organic carbon content.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffects of two nitrogen levels on soil carbon fractions under organic and conventional cultivation\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"12\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSoil layer\u003c/p\u003e \u003cp\u003e(cm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTreatment\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eTOC\u003c/p\u003e \u003cp\u003e(g/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c8\" namest=\"c6\"\u003e \u003cp\u003eDOC (g/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c11\" namest=\"c9\"\u003e \u003cp\u003e(AOC) (g/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eHS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e0\u0026ndash;10 cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCFN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e20.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e25.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.42a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.79a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e82.75\u0026thinsp;\u0026plusmn;\u0026thinsp;3.65b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e102.35\u0026thinsp;\u0026plusmn;\u0026thinsp;2.95b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e101.30\u0026thinsp;\u0026plusmn;\u0026thinsp;3.00c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e6.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e7.64\u0026thinsp;\u0026plusmn;\u0026thinsp;0.19b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e6.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCFN18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e24.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.83a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e28.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.71a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e25.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.53a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e93.20\u0026thinsp;\u0026plusmn;\u0026thinsp;3.10b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e102.55\u0026thinsp;\u0026plusmn;\u0026thinsp;1.75b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e109.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.80c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e6.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e7.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e6.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOFN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e25.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e26.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e27.64\u0026thinsp;\u0026plusmn;\u0026thinsp;0.78a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e135.90\u0026thinsp;\u0026plusmn;\u0026thinsp;3.20a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e122.30\u0026thinsp;\u0026plusmn;\u0026thinsp;2.00a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e139.45\u0026thinsp;\u0026plusmn;\u0026thinsp;1.35b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e7.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e8.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e8.87\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOFN18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e26.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e27.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e142.25\u0026thinsp;\u0026plusmn;\u0026thinsp;3.65a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e129.55\u0026thinsp;\u0026plusmn;\u0026thinsp;1.25a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e156.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.85a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e7.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e8.97\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e9.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e10\u0026ndash;20 cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCFN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.39a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e19.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e60.45\u0026thinsp;\u0026plusmn;\u0026thinsp;3.65c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e53.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e73.25\u0026thinsp;\u0026plusmn;\u0026thinsp;3.05a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e4.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e6.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e6.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCFN18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.78\u0026thinsp;\u0026plusmn;\u0026thinsp;0.66a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.91a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e14.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.55b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e70.15\u0026thinsp;\u0026plusmn;\u0026thinsp;2.15bc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e67.35\u0026thinsp;\u0026plusmn;\u0026thinsp;1.65b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e71.80\u0026thinsp;\u0026plusmn;\u0026thinsp;2.40a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e5.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34bc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e6.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e6.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOFN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e18.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e19.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e14.46\u0026thinsp;\u0026plusmn;\u0026thinsp;1.10b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e82.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e75.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e71.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e6.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.19ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e6.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e6.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOFN18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e18.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.64a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e18.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.66a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e87.85\u0026thinsp;\u0026plusmn;\u0026thinsp;1.75a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e72.50\u0026thinsp;\u0026plusmn;\u0026thinsp;2.10a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e70.40\u0026thinsp;\u0026plusmn;\u0026thinsp;1.55a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e6.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e7.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e6.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e0\u0026ndash;10 cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e5.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e11.08*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e224.64**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e127.21**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e595.74**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e18.51*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e27.18**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e245.13**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28.35**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e9.90*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e54.21**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e4.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e6.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u0026times;N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e148.57**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e6.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e10\u0026ndash;20 cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e76.74**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e101.66**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e47.86**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e53.39**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e12.73*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e10.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e18.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e4.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e13.32*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e6.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u0026times;N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e44.26**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e38.98**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e3.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe data is presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD. Different lowercase letters within the same column indicate significant differences (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) among the four treatments. TOC, Soil total carbon; DOC, Soil dissolved organic carbon; AOC, Soil acid hydrolysis organic carbon. TS, Tillering stage; HS, Heading stage; MS, Maturing stage; F, Cultivation pattern; N, Nitrogen application level; F \u0026times; N, Interaction between cultivation mode and nitrogen level.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eSoil nitrogen pool\u003c/h2\u003e \u003cp\u003eAs shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, total nitrogen content in soil surface is significantly higher than subsurface during all three periods. Differences between treatments are evident in tillering and heading stages but disappear in maturity stage. Under same nitrogen level, surface and subsurface total nitrogen is influenced by cultivation methods. Tillering stage shows OF\u0026thinsp;\u0026gt;\u0026thinsp;CF; pattern reverses after tillering. After tillering, total nitrogen in different layers is influenced by nitrogen levels. After tillering, under same cultivation method, N12 treatment increases total nitrogen in surface soil. For example, at heading stage, OFN18 total nitrogen is 14.22% higher than OFN12 in surface soil; conversely, OFN12 in subsurface soil is 23.33% higher than OFN18.\u003c/p\u003e \u003cp\u003eOverall, alkali-hydrolyzable nitrogen content in soil surface is much higher than subsurface. Its content is influenced by various factors during different periods. At tillering stage, surface alkali-hydrolyzable nitrogen is influenced by nitrogen levels (N12\u0026thinsp;\u0026gt;\u0026thinsp;N18). Under CF and OF, N12 treatment has 11.69% and 34.88% higher content than N18 treatment in surface soil respectively, with significant difference under OF. No significant differences in subsurface. At heading stage, no significant differences in surface; subsurface shows N12\u0026thinsp;\u0026gt;\u0026thinsp;N18. At maturity stage, alkali-hydrolyzable nitrogen is mainly influenced by cultivation methods. N12 significantly increases soil alkali-hydrolyzable nitrogen before maturity stage. OFN12 shows more significant increase.\u003c/p\u003e \u003cp\u003eSoil ammonium nitrogen is significantly influenced by cultivation methods, nitrogen levels, and their interaction (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). Surface soil and N12 treatment in subsurface show trend of initially decreasing then increasing ammonium nitrogen content, especially at tillering stage. Differences between soil layers only at tillering stage. At maturity stage, due to interaction, CFN12 and OFN18 treatments have higher ammonium nitrogen content. In subsurface soil, compared to CFN18 treatment, CFN12 shows 46.97% increase; compared to OFN18 treatment, it shows 55.36% increase.\u003c/p\u003e \u003cp\u003eCompared to surface soil, nitrate nitrogen content in subsurface shows less fluctuation (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). At tillering stage, CFN12 and OFN18 treatments have higher nitrate nitrogen content but lose advantage after tillering. After heading stage, high nitrogen levels promote nitrate nitrogen. Surface soil shows N18\u0026thinsp;\u0026gt;\u0026thinsp;N12. During heading and maturity stages, under conventional and organic cultivation, N18 treatment has higher nitrate nitrogen content than N12 treatment. Data indicates CFN12 and OFN18 are advantageous at tillering stage; after tillering, nitrate nitrogen in surface soil increases with nitrogen input.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEffects of two nitrogen levels on soil nitrogen fractions under organic and conventional cultivation\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"15\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSoil layer (cm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTreatment\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c5\" namest=\"c3\"\u003e \u003cp\u003eSoil total nitrogen (STN) (g/kg)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c8\" namest=\"c6\"\u003e \u003cp\u003eSoil alkali-hydrolyzable nitrogen (SAN) (g/kg)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c11\" namest=\"c9\"\u003e \u003cp\u003eSoil nitrate nitrogen NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e (mg/kg)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"3\" nameend=\"c14\" namest=\"c12\"\u003e \u003cp\u003eSoil ammonium nitrogen NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e (mg/kg)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"1\" nameend=\"c15\" namest=\"c15\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eHS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003eTS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003eHS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e0-10cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCFN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e173.27\u0026thinsp;\u0026plusmn;\u0026thinsp;3.26ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e164.78\u0026thinsp;\u0026plusmn;\u0026thinsp;3.10a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e178.91\u0026thinsp;\u0026plusmn;\u0026thinsp;1.90b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e 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align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOFN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.58\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.62\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e116.77\u0026thinsp;\u0026plusmn;\u0026thinsp;0.89a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e141.15\u0026thinsp;\u0026plusmn;\u0026thinsp;1.38a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e116.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.37b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.70\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01ab\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e17.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.50b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e17.54\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e16.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOFN18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e117.09\u0026thinsp;\u0026plusmn;\u0026thinsp;2.70a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e117.77\u0026thinsp;\u0026plusmn;\u0026thinsp;2.36bc\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e105.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e0.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01c\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e0.87\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e0.87\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01b\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e19.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.64a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e16.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.51a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e16.52\u0026thinsp;\u0026plusmn;\u0026thinsp;0.47a\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e0-10cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13.34*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e56.10**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e19.05*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e85.71**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e410.83**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e69.42**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e6.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e7.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e2.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40.60**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.29*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10.72*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e26.90**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e5.07\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e110.23**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e255.01**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e1.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e95.511**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e54.607**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u0026times;N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e33.84**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e6.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e3.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e7.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2306.38**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e94.260**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e3107.97**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e119.832**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e4.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e1.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e10-20cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.93*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e9.22*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e5.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e170.98**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e13.53*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e70.89**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e23.45**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e5.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e0.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e11.36*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e23.81**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e54.70**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e9.51*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e67.70**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e858.12**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e268.84**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e8.059*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e5.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u0026times;N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11.26*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e2.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e402.08**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e3.41\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e1985.11**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e1619.28**\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e11.738*\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e0.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe data is presented as mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD. Different lowercase letters within the same column indicate significant differences (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) among the four treatments. TS, Tillering stage; HS, Heading stage; MS, Maturing stage; F, Cultivation pattern; N, Nitrogen application level; F \u0026times; N, Interaction between cultivation mode and nitrogen level.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eSoil humus\u003c/h2\u003e \u003cp\u003eDuring the tillering stage, the proportion of humic acid organic carbon content in soil humus is higher compared to other stages, ranging from 39.25\u0026ndash;75.87% (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). After the tillering stage, organic carbon is mainly provided by humin, accounting for 52.93\u0026ndash;71.65%, which is notably significant in the 0\u0026ndash;10 cm soil layer. In the 0\u0026ndash;10 cm soil layer during the heading and maturity stages, compared to OFN18, the carbon content of humin in OFN12 is significantly increased by 13.36% and 17.78%, respectively, with significant differences observed. The fulvic acid content shows relatively minor fluctuations overall. The decrease in the proportion of humic acid carbon content after the tillering stage, compared to the tillering stage, is mainly due to the substantial increase in humin content. However, in the surface soil after the tillering stage, there is a significant increase in humic acid content, which is the main change in humic acid content. During the heading stage, the carbon content of humin in all treatments increased by more than 35%, with the most significant increase observed in the OF treatment. Surface soil humin acid is significantly influenced by cultivation methods after the tillering stage, showing OF\u0026thinsp;\u0026gt;\u0026thinsp;CF. Under conventional nitrogen application, the carbon content of humin acid in the OF treatment during the heading and maturity stages increased by 22.51% and 21.14%, respectively, compared to CF, and under the influence of N12, this increase was even higher, with significant differences observed. Additionally, in the surface soil after the tillering stage, compared to other treatments, OFN18 has a higher proportion of humic acid, reaching 39.11% during the heading stage and 37.38% during the maturity stage, indicating a higher conversion rate of organic carbon to humic acid in soil humus.\u003c/p\u003e \u003cp\u003eOverall, as the growth process advances, the significant increase in humin content leads to a decrease in the proportion of humic acid. Compared to conventional cropping systems, organic farming significantly increases the humic acid content in the 0\u0026ndash;20 cm soil layer, especially in the 0\u0026ndash;10 cm soil layer. Among them, the OFN18 treatment is more conducive to the conversion of organic carbon to humic acid.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003eSoil aggregates\u003c/h2\u003e \u003cp\u003eDuring the maturity stage, in all treatments, more than half of the soil aggregates are composed of macroaggregates with particle sizes larger than 2mm, with the remaining majority being microaggregates with particle sizes smaller than 0.106mm, accounting for 9\u0026ndash;22% (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMacroaggregates with particle sizes larger than 2mm are predominantly influenced by cultivation methods, with a notable trend of OF\u0026thinsp;\u0026gt;\u0026thinsp;CF, particularly evident in the surface OF treatment. In the surface soil under N18, the content of macroaggregates larger than 2mm in OF is increased by 12.36% compared to CF, which decreases to 6.95% under N12, both showing significant differences. In the surface layer, the proportion of microaggregates with particle sizes between 0.106-0.25mm is higher in OF than in CF; however, in the subsoil layer, the trend is reversed, with CF\u0026thinsp;\u0026gt;\u0026thinsp;OF, and the differences are significant. In the surface layer, the proportion of microaggregates with particle sizes smaller than 0.106mm is influenced by cultivation methods, showing CF\u0026thinsp;\u0026gt;\u0026thinsp;OF; in the subsoil layer, influenced by nitrogen levels, it is N18\u0026thinsp;\u0026gt;\u0026thinsp;N12. Among all treatments, OFN12 has the smallest proportion of microaggregates with particle sizes smaller than 0.106mm.\u003c/p\u003e \u003cp\u003eIn summary, soil aggregates of different particle sizes are influenced by different factors. However, in the 0-20cm soil layer, the proportion of macroaggregates larger than 2mm is higher in the OF treatment, with OFN12 treatment showing a higher proportion of macroaggregates larger than 0.25mm. Therefore, the structural integrity of water-stable aggregates, particularly under OFN12 treatment, is more rational, facilitating better regulation of soil aeration, water retention, nutrient preservation, and fertility release in field soils.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003eSoil Enzyme Activity\u003c/h2\u003e \u003cp\u003eThe effects of different cropping systems and nitrogen levels on three soil enzyme activities in the surface and subsurface soils at maturity are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.Soil sucrase, a hydrolytic enzyme, catalyzes sucrose hydrolysis. In the mature stage of rice, surface soil sucrase activity is significantly higher than subsurface, especially under OF treatment. In surface soils, sucrase activity of CFN12 treatment lags. Under N12 levels, sucrase activity under OFN12 is higher than CF. Surface soil sucrase is affected by cultivation method and nitrogen application rate interaction. In subsurface soils, sucrase activity shows N12\u0026thinsp;\u0026gt;\u0026thinsp;N18. Under CF and OF, N12 treatment has sucrase activity 40.62% and 55.93% higher than N18 treatment respectively. N18 inhibits sucrase in subsurface. OFN12 is more conducive to soil enzyme-catalyzed reactions.\u003c/p\u003e \u003cp\u003eSoil cellulase activity reflects carbon cycle. Except for OFN12 treatment, subsurface has higher cellulase activity. In mature surface soils, OFN12 treatment has the highest cellulase activity, 32.71% higher than OFN18 treatment. In subsurface soils, cellulase activity is influenced by cultivation method and nitrogen level (OF\u0026thinsp;\u0026gt;\u0026thinsp;CF, N18\u0026thinsp;\u0026gt;\u0026thinsp;N12). Only CFN12 treatment has significantly lower activity. OFN12 shows higher activity in both surface and subsurface.\u003c/p\u003e \u003cp\u003eSoil leucine aminopeptidase activity helps assess nitrogen cycling. Surface has higher activity than subsurface. Across depths, CF\u0026thinsp;\u0026gt;\u0026thinsp;OF, with OFN12\u0026thinsp;\u0026gt;\u0026thinsp;OFN18\u0026thinsp;\u0026gt;\u0026thinsp;CFN18\u0026thinsp;\u0026gt;\u0026thinsp;CFN12. Under OF treatment, leucine aminopeptidase activity is significantly higher than CF. Under N12, in 0\u0026ndash;20cm soil layer, OF treatment enzyme activity is 34.47% and 49.95% higher than CF. Under N18, increase narrows. Under OF, N12 has 10.16% and 11.23% higher leucine aminopeptidase activity than N18 in 0\u0026ndash;20cm soil layer. OFN12\u0026thinsp;\u0026gt;\u0026thinsp;N18 under OF.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003eCorrelation analysis of soil indicators\u003c/h2\u003e \u003cp\u003eTaking mature soil samples as an example, Pearson algorithm was used to analyze the correlation among 15 physicochemical indicators including total nitrogen (TN), alkali-hydrolyzable nitrogen (AHN), ammonium nitrogen (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N), nitrate nitrogen (NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N), total phosphorus (TP), available phosphorus (AP), organic matter (OM), pH, total carbon (TC), soil organic carbon (SOC), dissolved organic carbon (DOC), acid extractable organic carbon (AOC), sucrase (SUC), leucine aminopeptidase (LAP), and cellulase (CEL). The results are shown in Fig.\u0026nbsp;5. Overall, in the surface soil, except for pH, mineral nitrogen content influenced by pH, and slightly lower total phosphorus content, all other fertility, carbon, nitrogen, and enzyme activity indicators showed significant or extremely significant positive correlations. Particularly, the positive correlation was more pronounced in the soil carbon pool-related indicators.\u003c/p\u003e \u003cp\u003eIn this study, compared to the subsoil, the relationship between fertility indicators, active carbon and nitrogen indicators, and enzyme activity is closer in the surface soil, and their mutual promotion effect is more significant.\u003c/p\u003e \u003cp\u003e \u003cb\u003eFigure\u0026nbsp;5.\u003c/b\u003eCorrelation analysis of soil nutrients, enzyme activity, and active carbon and nitrogen in soil (A) 0\u0026ndash;10 cm;(B) 10\u0026ndash;20 cm\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003ePrincipal component analysis of soil indicators\u003c/h2\u003e \u003cp\u003eTaking mature soil samples as an example, principal component analysis was conducted on the 21 physicochemical indicators including TN, AHN, NH4+-N, NO3\u0026ndash;N, TP, AP, OM, pH, TC, SOC, DOC, AOC, SUC, LAP, CEL, fulvic acid (FA), humic acid (HA), humin (HM), proportion of different aggregate sizes (\u0026gt;\u0026thinsp;2 mm, 0.25-2 mm, \u0026lt;\u0026thinsp;0.25 mm). The results are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e, where the cumulative variance contribution rates of the major components PC1 and PC2 reached 72.4% and 64.6% in the surface and subsoil, respectively, explaining the differences among the four treatments well. Scores on PC1 and PC2 were calculated for each treatment to represent soil properties comprehensively. The ranking of treatments in the 0-10cm soil depth was(Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e): OFN12\u0026thinsp;\u0026gt;\u0026thinsp;OFN18\u0026thinsp;\u0026gt;\u0026thinsp;CFN18\u0026thinsp;\u0026gt;\u0026thinsp;CFN12; and in the 10-20cm depth, it was OFN12\u0026thinsp;\u0026gt;\u0026thinsp;OFN18\u0026thinsp;\u0026gt;\u0026thinsp;CFN12\u0026thinsp;\u0026gt;\u0026thinsp;CFN18. The scores showed that OF\u0026thinsp;\u0026gt;\u0026thinsp;CF in both soil depths, with N18\u0026thinsp;\u0026lt;\u0026thinsp;N12.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a), in the surface soil, the active carbon index had positive effects on enzyme activity, organic matter content, some active nitrogen indices, and the proportion of aggregate sizes\u0026thinsp;\u0026gt;\u0026thinsp;0.25 mm to varying degrees. The input of organic materials significantly improved some soil fertility indicators and the active carbon index while reducing the proportion of aggregate sizes\u0026thinsp;\u0026lt;\u0026thinsp;0.25 mm. Notably, when moderate organic fertilizer was applied, organic matter, enzyme activity, and the proportion of 0.25-2 mm aggregates increased significantly. Enzymatic reactions were enhanced in a more suitable organic matter environment for microbial growth, with excellent enzyme activity in OFN12. Excessive organic fertilizer input led to an increase in the active nitrogen index and the proportion of aggregates\u0026thinsp;\u0026gt;\u0026thinsp;2mm, favoring humic acid derivatives. In the subsoil (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b)), the overall advantage of soil indicators in OFN12 was slightly lower than in the surface soil. The impact of organic materials on soil organic matter content, active carbon and nitrogen indices, enzyme activity, humic acid proportion, and large aggregates in the subsoil was not as significant as in the surface soil, depending on the input amount.\u003c/p\u003e \u003cp\u003eIn conclusion, compared to conventional cultivation, organic cultivation improved soil properties and facilitated soil improvement while promoting cultivation. OFN12 showed a significant improvement in specific soil indicators such as enzyme activity and carbon pool indices, while OFN18, although less pronounced in increasing soil indicators than OFN12, had a more comprehensive promotion effect on multiple indicators. Specifically, in the surface soil, the synergistic effect of organic cultivation and reduced nitrogen fertilization yielded the best improvement results.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eIntegrated scores of soil indicators for different treatments\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSoil layer\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTreatment\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePC1\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePC2\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eTotal points\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRank\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e0\u0026ndash;10 cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCFN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-3.5306\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-0.50979\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-4.04039\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCFN18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-2.44123\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.709985\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-1.73125\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOFN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e3.149705\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.59166\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.741365\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOFN18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.82213\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-2.79186\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.03027\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e10\u0026ndash;20 cm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCFN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-4.27673\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e1.25186\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-3.02487\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCFN18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.0382\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-3.49288\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-3.45468\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOFN12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e2.494955\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e2.32264\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e4.817595\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOFN18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e1.743565\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-0.08163\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e1.66194\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003eInfluence of organic cultivation and reduced nitrogen fertilization on soil carbon and nitrogen pools\u003c/h2\u003e \u003cp\u003eAlthough the response mechanisms of various soil organic carbon fractions to fertilization measures may vary, previous studies have shown that overall, heavy use of chemical fertilizers and biased nitrogen application may inhibit soil organic carbon and active organic carbon content\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e,\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. In this experiment, the surface soil organic carbon content under the CFN18 treatment was higher before the maturity period, while the OFN12 treatment could maintain soil organic carbon content at a higher level across all three periods, indicating overall higher soil fertility under this treatment. This may be attributed to the low carbon-to-nitrogen ratio in the soil due to nitrogen fertilizer application, promoting organic matter decomposition\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. As the experimental plots were paddy fields in the early to mid-growth periods of rice, compared to upland areas, the soil organic matter has less contact with the external environment, and the anaerobic nature of organic carbon in the soil makes the carbon-to-nitrogen ratio and organic carbon content more stable. Therefore, the CFN18 treatment could maintain a good organic carbon content before the maturity period, but during the field drying at maturity, a large amount of organic carbon began to decompose upon contact with air, consistent with previous research findings.\u003c/p\u003e \u003cp\u003eAs one of the active components of soil carbon pools\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e, soluble organic carbon, due to its dissolution characteristics under certain conditions, can rapidly move in soil and water bodies\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e, facilitating microbial mineralization and crop root absorption\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. Soluble organic carbon includes water-soluble organic carbon, organic acids, humic acids, and other complex components primarily provided by plant residues, organic materials, and soil humus \u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. This study found that except for the subsoil, the soluble organic carbon content under organic cultivation was significantly higher than conventional cultivation, indicating that organic cultivation could provide a large amount of highly efficient and easily absorbable active organic carbon components for plants. However, by the time of field drying at maturity, the soluble organic carbon in the subsoil was significantly depleted. This suggests that organic cultivation, organic fertilization, cultivation practices, and soil physical properties may directly enhance the content of active organic carbon sensitive to external changes.\u003c/p\u003e \u003cp\u003eAcid-extractable organic carbon represents the content of proteins\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e, polysaccharides, and ribose in the soil through partial hydrolysis by hot concentrated hydrochloric acid(Xu et al., 1997). Proteins mainly originate from soil organic matter and can be degraded by microorganisms to form amino acids\u003csup\u003e\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u003c/sup\u003e; polysaccharides provide energy for soil organisms and crops, promoting microbial reproduction and enhancing microbial metabolic activity and organic matter production, thus improving soil fertility\u003csup\u003e\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. High protein and polysaccharide content form a beneficial cycle, where rich organic matter provides a good living environment for microorganisms \u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e, reducing their competition with roots for nutrients. Compared to conventional cultivation, the results of this experiment show that organic cultivation significantly increased the content of acid-extractable organic carbon, indicating that organic fertilizers increased soil organic matter content, promoted soil microbial metabolism, and increased protein and polysaccharide content. These results demonstrate that organic cultivation can effectively enhance soil organic carbon content and active organic carbon content, helping to improve soil fertility and microbial activity levels.\u003c/p\u003e \u003cdiv id=\"Sec23\" class=\"Section3\"\u003e \u003ch2\u003eInfluence of organic cultivation and reduced nitrogen fertilization on soil aggregates and humus\u003c/h2\u003e \u003cp\u003eOne of the signs of soil degradation under continuous cropping is the loss of soil organic matter and a decrease in aggregate size, indicating that aggregates can characterize soil fertility \u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. In this experiment, the proportion of large aggregates with a size greater than 2 mm in both soil layers was significantly influenced by the cultivation method, showing organic\u0026thinsp;\u0026gt;\u0026thinsp;conventional. Under organic cultivation, the proportion of large aggregates with a size greater than 0.25 mm was higher, with the highest increase in the proportion of aggregates with a size of 0.5-1 mm in the N12 treatment. The improvement effect of organic cultivation on soil aggregates observed in the experiment is consistent with previous findings \u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eAs the main component of organic matter in aggregates, the formation and transformation of humus are crucial for maintaining the stability of aggregates \u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. Humus is involved in the formation of aggregates, promoting soil carbon storage function and enhancing carbon sequestration capacity\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e. Typically, compost can enhance soil fertility because the humus formed during composting effectively supplements the humus deficit caused by soil fertility consumption\u003csup\u003e\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e. Humic acid is a major component of humus, and different components of humic substances have varying effects on aggregate formation: the content of humic acid in humic substances is a key factor affecting aggregate stability, while the influence of fulvic acid is relatively minor \u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e. Research has shown that after adding different concentrations of humic acid to soil, the content of water-stable aggregates in soils with different degrees of erosion will increase\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn this experiment, there was no significant change in the fulvic acid content in the soil after the tillering stage, with limited impact on soil aggregates. Under organic cultivation conditions, the humic acid content in the soil at 0\u0026ndash;10 cm depth significantly increased, leading to a higher proportion of large aggregates with a size greater than 2 mm and greater than 0.25 mm at maturity. Organic cultivation has a positive effect on increasing humic acid content and promoting the process of aggregate formation, significantly increasing the proportion of large aggregates, especially evident in the OFN12 treatment at maturity. The impact of different nitrogen fertilizer levels on aggregates and humus was relatively small, but a reasonable nitrogen fertilizer level combined with organic cultivation can have a positive effect on the structure of aggregates and humus composition.\u003c/p\u003e \u003cp\u003eIn summary, organic cultivation significantly increases the humic acid content and the proportion of humic acid, improving the structure of soil aggregates, promoting soil carbon storage, and avoiding the decrease in aggregate size and soil loss issues after repeated tillage.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003eImpact of organic cultivation and reduced nitrogen fertilization on soil enzyme activity\u003c/h2\u003e \u003cp\u003eThis study demonstrated that organic cultivation significantly increased the activity of sucrase, leucine aminopeptidase, and cellulase in the soil, especially in the mature stage of the surface soil. This increase may be related to the use of the previous crop, milk vetch, in the experiment. The decomposition of milk vetch provided abundant organic matter and a suitable microenvironment, promoting microbial reproduction and activity in the soil, thereby enhancing soil microbial activity and enzyme activity. This is consistent with previous research findings that green manure can increase the activity of enzymes involved in nitrogen cycling\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e. Additionally, the reduced nitrogen fertilization measures adopted in organic cultivation also showed positive effects, especially in increasing the activity of leucine aminopeptidase in the soil. This improvement may be related to the imbalance in microbial community structure caused by the reduction of excess nitrogen \u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn conclusion, organic cultivation and reduced nitrogen fertilization measures have a significant impact on the enhancement of soil enzyme activity, providing favorable conditions for the growth and activity of soil microbial communities, thereby contributing to maintaining soil health and biological activity.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eOrganic cultivation combined with moderate nitrogen reduction treatments increased the TOC, SOC, DOC, AOC, and AHN content across different stages. Soil enzyme activities in the plough layer were significantly influenced by the cultivation method, with organic cultivation surpassing conventional methods. Organic cultivation notably enhanced humic acid content in the 0\u0026ndash;10 cm soil layer compared to conventional cultivation. This increase in humic acid content promoted the aggregation of macroaggregates in the plough layer. Comprehensive soil fertility assessments indicated that organic treatments outperformed conventional treatments, and appropriate nitrogen reduction fertilization were superior to conventional nitrogen applications. These findings illuminate a promising avenue for sustainable agricultural solutions, underscoring closer associations and superior integrated effects among soil carbon and nitrogen pools, enzyme activities, and nutrient contents under organic cultivation combined with appropriate nitrogen reduction fertilization. Continued research into these cultivation patterns combined with varying nitrogen application rates holds promise for improving cultivated land quality and promoting sustainable rice cultivation, paving the way for optimal nitrogen application rates and cultivation methods to enhance soil fertility sustainably and achieve high rice yields.\u003c/p\u003e"},{"header":"Declarations","content":" \u003cp\u003e \u003cstrong\u003eCompeting interests\u003c/strong\u003e \u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eG.W.: Writing \u0026ndash; original draft, Data curation, Formal analysis,Resources. Y.C.: Conceptualization, Data curation, Methodology. Y.C.: Writing \u0026ndash; review \u0026amp; editing. X.H.: Data curation, Resources. S.Y.: Data curation, Resources. M.J.: Writing \u0026ndash; review \u0026amp; editing. Z.Z.: Funding acquisition, Methodology, Supervision. L.H.: Project administration, Funding acquisition Supervision, Validation, Writing \u0026ndash; review \u0026amp; editing. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThis work was supported by Special Funds for Scientific and Technological Innovation of Jiangsu province, China (BK20220017) and Jiangsu Province Postgraduate Research Innovation Program (KYCX24-3785).We thank all the colleagues of Yangzhou Mabangwan Ecological Agricultural Science and Technology Co. for their help during the experimental field.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data generated or analysed during this study are included in this published article.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eKhan, Z., Zhang, K., Khan, M. N., Zhu, K. \u0026amp; Hu, L. 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Intercropping-driven nitrogen trade-off enhances maize productivity in a long-term experiment. \u003cem\u003eField Crops Res.\u003c/em\u003e \u003cb\u003e287\u003c/b\u003e, 108671 (2022).\u003c/span\u003e\u003c/li\u003e \u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Organic cultivation, Soil carbon and nitrogen pools, Soil aggregates, Humic composition, Enzyme activity","lastPublishedDoi":"10.21203/rs.3.rs-5163192/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5163192/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWith the development of intensive agriculture, soil health issues has received widespread attention. However, the mechanism of response to soil carbon and nitrogen pool sequestration characteristics under different cultivation practices in combination with nitrogen application is not yet elucidated. This limits the idea of trying to improve the soil biosystem in paddy fields through organic cultivation combined with appropriate nitrogen reduction fertilization. A split-plot design was employed, with cultivation methods (organic cultivation [OF] and conventional cultivation [CF]) and nitrogen levels (pure nitrogen at 180 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e [N12] and pure nitrogen at 270 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e [N18]) combined into four treatments. The impacts of organic and conventional cultivation as well as different nitrogen fertilizer application rates on soil properties were compared. The results demonstrated that organic cultivation combined with appropriate nitrogen reduction significantly increased the total carbon content of the surface soil and significantly increased the organic carbon content in the soil. Soil ammonium nitrogen content showed an overall trend of decreasing and then increasing, while the opposite was true for soil nitrate nitrogen content. Notably, the organic cultivation increased the activity of enzymes involved in the carbon and nitrogen cycle and the content of humic acid in the tillage layer, which led to the improvement of the soil aggregate structure.This research indicates that organic cultivation combined with appropriate nitrogen reduction fertilization positively affects soil carbon and nitrogen pool characteristics. This study provides new insights for restoring soil fertility and promoting sustainable agriculture.\u003c/p\u003e","manuscriptTitle":"Optimizing effects of organic farming and moderately low nitrogen levels on soil carbon and nitrogen pools, humus composition and related enzyme activities","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-26 18:46:14","doi":"10.21203/rs.3.rs-5163192/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"f28c6cc9-649c-471b-9d21-93c9277399fc","owner":[],"postedDate":"November 26th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":40072049,"name":"Earth and environmental sciences/Ecology"},{"id":40072050,"name":"Earth and environmental sciences/Environmental sciences"}],"tags":[],"updatedAt":"2024-12-23T05:38:46+00:00","versionOfRecord":[],"versionCreatedAt":"2024-11-26 18:46:14","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5163192","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5163192","identity":"rs-5163192","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}