Effects of fermented biogas slurry returning of tail vegetables on soil enzyme activity and fertility

Effects of fermented biogas slurry returning of tail vegetables on soil enzyme activity and fertility | 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 Effects of fermented biogas slurry returning of tail vegetables on soil enzyme activity and fertility Shuzhi Yue, Bian Liu, Huang Jie, Run Chu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4333390/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 Objective The objective of this study is to study the effects of fermented biogas slurry derived from tail vegetables on soil physicochemical properties and enzyme activities, and to evaluate soil fertility. Method Baby cabbage cultivated in the field, five treatments with iso-nitrogen fertilization were set up: CK (no biogas liquid nitrogen), T1 (25% biogas liquid nitrogen), T2 (50% biogas liquid nitrogen), T3 (75% biogas liquid nitrogen) and T4 (100% biogas liquid nitrogen). Results It was found that returning biogas slurry from the fermentation of tail vegetables to the field significantly increased soil organic matter, total nitrogen, alkaline dissolved nitrogen, available phosphorus, available potassium, and microbial carbon (nitrogen) content, improved soil porosity and decreased soil bulk density, with little effect on soil water content; Fermentation of biogas slurry from tail cabbage significantly increased the activities of urease, sucrase and alkaline phosphatase, but had little effect on catalase activity, and the increases of urease, sucrase and phosphatase activities were 3.49%~21.83%, 8.71%~22.29% and 1.95%~10.38%, respectively. Through principal component cluster analysis, the weighted comprehensive score was used as a new index, and soil fertility was comprehensively evaluated as T3>T2> T4>T1>CK. Conclusion Considering the comprehensive effects of fermented biogas slurry fertilization on soil physicochemical properties and soil enzyme activities, the fertilization effect T3 (246m3·hm-2 tail vegetable fermentation biogas slurry + 44kg·hm-2 pure chemical nitrogen) was the best and the comprehensive fertility was the best. Biological sciences/Ecology Biological sciences/Plant sciences fermented biogas slurry of tail vegetables enzyme activity soil fertility Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 6 Introduction Soil fertility is the cornerstone of excellent crop growth and germplasm characteristics, and it has received more and more attention. The application of chemical fertilizers is a double-edged sword; rational application can increase crop yields, while excessive application damages the ecological environment and affect crop yields. At present, the amount of chemical fertilizer used in China's agricultural production remains high, and the output of grain per unit of chemical fertilizer and the quality of agricultural products are declining year by year[1]. In production, producers only pay attention to chemical fertilizers, ignore the relationship between soil physical and chemical factors, soil enzyme activities and soil structure, and over rely on chemical fertilizers, which leads to a series of problems such as soil acidification, compaction, attenuation of enzyme activity, crop yield reduction and loss of soil quality [2,3]. Soil enzymes originate from the metabolism of soil plants, animals, plants and microorganisms [4], mark the dynamics of soil development and evolution and are one of the most important indicators for assessing soil fertility [5].Urease activity reflects the soil nitrogen status [6], phosphatase activity reflects the amount of phosphorus that can be absorbed and utilized by plants [7],catalase activity reflects the ability of roots to eliminate peroxide toxicity [8] and sucrase activity reflects the level of energy and carbon sources provided by soil for crop growth [9]. Plateau summer vegetables are a specialty industry in Gansu Province, with the area under vegetable cultivation increasing by 19,000 hm2 and production increasing by 4.9% by 2022 compared to the previous year[10]. Tail vegetables are waste products generated during the production and processing of vegetables, and are usually accumulated as household waste. Vegetable wastes have high moisture content and if they are piled indiscriminately, they can easily rot, breed mosquitoes and flies, spread germs [11,12] and even lead to clogging of water channels [13]. In addition, the liquid leaking from the accumulation of vegetable wastes can flow into the river, causing water pollution problems. The results showed that the contents of total nitrogen, total phosphorus, and total potassium and C/N were 1.96%~5.39%, 0.35%~1.82%, 0.80%~5.42%, and 6.70~20.35, respectively in tail vegetables, which had high fertilizer utilization value [14],and unreasonable disposal would not only pollute the environment, but also cause waste of resources[13].The remaining liquid (biogas slurry) generated from the anaerobic fermentation of tail vegetables can be returned to the field as fertilizer[15,16], which not only enables the recycling of tail vegetable resources, but also reduces environmental risks and planting costs. This approach is in line with China's development requirements to promote green and circular agriculture. At present, there have been a large number of studies on fertilization with biogas slurry, and the results show that the application of biogas slurry can improve the physical and chemical properties of the soil and increase yield and quality of crops. However, the existing studies mainly focus on biogas slurry from livestock and poultry manure biogas slurry, and there are relatively few studies on the utilization of biogas slurry from fermented tail vegetables. However, the efficient use of tail vegetable waste is of great value to limit the expansion of vegetable production areas. The purpose of this study was to analyze the effect mechanism of biogas slurry application on the physicochemical properties of soil and enzyme activities in the process of cultivating baby cabbage in the field. Based on the correlation between the two factors, principal component-cluster analysis will be used to evaluate the impact of biogas slurry returning on soil fertility by using the comprehensive score as a new evaluation index. The purpose of this study is to provide a theoretical basis for the appropriate dosage of fermented biogas slurry of tail vegetables to return to the field and to provide theoretical support for the treatment of tail vegetables in vegetable cultivation areas. Materials and methods 1.1 Overview of the test site The trial was conducted from May to July 2023 at Yuansheng Agriculture and Animal Husbandry Co. Ltd. (38°27′N, 102°09′E), Yongchang County, Gansu Province. The area is characterized by a temperate, arid climate with a large temperature difference between day and night. The average effective accumulated temperature (≥ 10°C) is 2011°C, the frost-free period is about 134 days, the average annual temperature is 4.8°C, the average annual precipitation is 185 mm, and the total annual evaporation is 2000.6 mm. The properties of the tested soil are listed in Table 1 . Table 1 Physical and chemical properties of test soil component pH SO(g· kg − 1 ) TN(g· kg − 1 ) AN(g· kg − 1 ) TP(g· kg − 1 ) AP(g· kg − 1 ) AK(g· kg − 1 ) content 7.8 22.91 1.24 0.072 0.196 0.029 20.49 Note:pH-pH;SOM-organic matter;TN-total nitrogen;AN-alkaline nitrogen;TP-total phosphorus;AP-quick-acting phosphorus; AK-quick-acting potassium. 1.2 Test Materials The test crop was baby cabbage with a growth period of about 60 days, a plant height of about 20 cm and a ball diameter of about 10 cm. The organic matter in the tested biogas slurry was 16.271g·kg − 1 , total nitrogen 0.532 g·kg − 1 , total phosphorus 0.028 g·kg − 1 , total potassium 1.99 g·kg − 1 , and the pH was 7.35. The tested fertilizers included urea (46% nitrogen), superphosphate (18% P 2 O 5 ) and potassium sulfate (50% K 2 O). 1.3 Design of Experiments In the experiment, an open-field direct mulching drip irrigation system was used. The area of the plot is 20 m2 (6.45×3.1 m), the row spacing of baby cabbage is 25×30 cm, and 125,000 plants are planted per hectare. The design principle of the application rate of biogas slurry was to meet the nitrogen demand of baby cabbage. The application rate was calculated according to the nitrogen content in the biogas slurry to ensure that each fertilization treatment is carried out under isonitrogen conditions. It was calculated that the potassium requirement was met in the case of nitrogen requirement, but the phosphorus was insufficient, and a one-time application of superphosphate as a base fertilizer was required. According to the planting experience of local vegetable farmers, baby cabbage requires 174 kg of pure nitrogen, 180 kg of pure phosphorus and 108 kg of pure potassium per hectare. Five isonitrogen fertilization treatments were established: CK (100% chemical nitrogen), T1 (25% biogas slurry nitrogen + 75% chemical nitrogen), T2 (50% biogas slurry nitrogen + 50% chemical nitrogen), T3 (75% biogas slurry nitrogen + 25% chemical nitrogen) and T4 (100% biogas liquid nitrogen) (see Table 2 for details). Each treatment consisted of three replicates, randomly arranged and surrounded by guard rows. According to the local fertilization experience, the amount of fertilizer applied before sowing (May 28) was 17% of the total amount (calculated as nitrogen fertilizer), 45% at seedling stage (June 12), 14% at rosette stage (June 23), 10% at the early stage of balling (July 1), and 14% at the middle stage of balling (July 11). At the same time, in addition to the irrigation, the water introduced by the biogas slurry was removed during the irrigation process, and the insufficient part was compensated with clean water to ensure that the irrigation amount of the experimental plot was consistent. Field management and other farming activities in the experiment were managed in a unified manner. Table 2 Input of biogas slurry to replace nitrogen fertilizer Treatment Nitrogen supply from biogas slurry( kg·hm − 2 ) Nitrogen supply fromchemical fertilizers( kg·hm − 2 ) Total nitrogen application rate ( kg·hm − 2 ) CK 0 174 174 T1 43 131 174 T2 87 87 174 T3 130 44 174 T4 174 0 174 1.4 Sample collection and analysis methods Soil samples were collected at the seedling stage (June 18), rosette stage (June 29), early balling stage (July 7), mid-balling stage (July 17) and harvest stage (August 1). The “S” type 5-point sampling method was used to collect soil samples from 0–20 cm soil layer, mixed evenly, and about 500g of soil samples were taken and divided into two parts. One sample was air-dried, ground, and sieved through a 2 mm and a 0.15 mm sieve for later use. The other fresh soil samples were stored in a freezer at 4°C for the determination of soil enzyme activity, with sampling and pretreatment completed within 24 hours. The physicochemical properties of the soil were determined according to the method described in Bao [ 17 ]. Soil bulk density, saturated water conductivity and total porosity were determined by the ring knife method. Potassium dichromate-external heating method was used to determine soil organic matter, whiles alkali hydrolysis diffusion method was used to determine alkali hydrolyzable nitrogen. Molybdenum-antimony resistance indicator method and flame photometer method were used to determine available phosphorus and available potassium respectively. The soil enzyme activity was determined according to the method of Guan et al[ 8 ]. Urease activity was determined by phenol-sodium hypochlorite colorimetric method, sucrase activity by 3,5-dinitrosalicylic acid colorimetric method, alkaline phosphatase activity by benzophthenic acid disodium phosphate colorimetric method, and catalase activity by potassium permanganate titration. The microbial biomass carbon was analyzed by chloroform fumigation-leaching[ 18 ], and TOC instrumental analysis. 1.5 Data processing and statistical analysis The experimental data were organized using Microsoft Excel 2010, and one-way ANOVA, correlation analysis (Pearson's index was used for size) and principal component analysis were performed using SPSS 26.0 (SPSS Inc., Chicago, IL, USA) statistical analysis software, and significant analysis of differences between treatments was performed using Duncan's new complex polarity method with a significance level of P < 0.05. Charts and graphs were generated by SPSS 26.0 and Origin 2021 software, respectively. Results and Analysis 2.1 Effect of biogas slurry returning on soil physicochemical factors It can be seen from Table 3 that biogas slurry application increased the contents of organic matter, total nitrogen, alkali hydrolyzable nitrogen, available phosphorus, available potassium and microbial biomass carbon/nitrogen (MBC/MBN), decreased the soil bulk density, and increased the total porosity. There was no significant difference in the soil moisture content among the treatments. Soil organic matter was increased in all growth cycles under the biogas slurry treatments, and the increase basically showed a trend of increasing with the increase of biogas application. The highest organic matter content was observed at the harvest stage, which increased by 6.24%, 15.20%, 22.77%, and 22.25% in the T1, T2, T3 and T4 treatments compared to CK, respectively. As the growing season progressed, total nitrogen showed an S-shaped trend of "increase-decrease-increase", and the range of change was positively correlated with the amount of biogas slurry returned to the field. Compared with the same period of CK, the total nitrogen content of T1, T2, T3 and T4 increased by 2.46%, 3.83%, 6.29%, 8.20%, 1.29%, 5.17%, 7.50% and 5.43%, respectively, and the total nitrogen in the early and middle stages of balling decreased and increased by 2.65%, 15.93% and 21.83% respectively in T1, T2, T3 and T4 and 24.49%. With the except of the harvest period, soil alkaline hydrolyzable nitrogen increased in all other growth cycles, and the increase was basically positively correlated with the amount of biogas slurry. The lowest soil alkaline dissolved nitrogen content was found at the seedling stage: T1, T2, T3 and T4 were increased by 1.93%, 4.86%, 5.81%, and 3.57%, respectively, compared to the CK treatment. The highest soil alkaline dissolved nitrogen content was found in the middle stage of nodulation: T1, T2, T3, and T4 were increased by 3.03%, 3.74%, 8.88%, and 5.83%, respectively, compared to the CK treatment. In general, the content of available phosphorus and available potassium in the soil decreased as the growth cycle progressed. Soil quick-acting phosphorus and quick-acting potassium contents increased with the increase in the amount of biogas slurry returned to the field in each growth cycle. Quick-acting phosphorus was highest at the seedling stage. Compared to CK, T1, T2, T3 and T4 increased by 4.23%, 15.01%, 17.31% and 19.56%, respectively, and lowest in the harvest stage, compared with CK, T1, T2, T3 and T4 increased by 5.46%, 15.05%, 18.11% and 6.89%, respectively. Quick-acting potassium content was the highest with T1, T2, T3 and T4 increasing by 3.11%, 17.72%, 21.08% and 28.38 compared to the CK. The carbon/nitrogen content of microbial biomass (MBC/MBN) initially increased and then decreased as the growth cycle progressed. At the initial stage of nodulation, the content of MBC and MBN was the highest, and T1, T2, T3 and T4 increased by 18.57%, 42.09%, 76.56%, 67.98% (MBC) and 22.27%, 49.50%, 104.94% and 93.00% (MBN), respectively. MBC content was lowest at the seedling stage with T1, T2, T3, and T4 increasing only by 5.60%, 8.27%, 10.27% respectively whiles MBN content was lowest at the harvest period, with the CK, T1, T2, T3, T4 increasing by 24.77%, 40.13%, 66.16%, 44.95%, respectively. The application of biogas slurry had no significant effect on soil moisture content, but some effects on soil bulk density and porosity. Except at the seedling stage, soil bulk density decreased, and porosity increased. The decrease and increase generally increase with increasing addition of biogas slurry. During the harvest period, the soil bulk density of T1, T2, T3 and T4 decreased by 2.62%, 4.59%, 5.46% and 6.55%, respectively, compared to CK. Table 3 Soil physicochemical factors under different fertilization treatments Period treatments SOM(g.kg − 1 ) TN(g.kg − 1 ) A(mg.kg − 1 ) AP(mg.kg − 1 ) AK(mg.kg − 1 ) MB(mg.kg − 1 ) MBN(mg.kg − 1 ) MC(%) SBD(g.cm − 3 ) TP(%) Seedling stage CK 19.79 ± 0.33b 1.22 ± 0.03b 72.85 ± 0.50b 36.76 ± 0.25d 184.45 ± e 127.87 ± 0.65d 21.25 ± 0.37d 0.15 ± 0.00a 1.49 ± 0.00a 0.42 ± 0.01ac T1 20.29 ± 0.18b 1.25 ± 0.00ab 74.53 ± 0.56b 38.31 ± 0.51c 223.26 ± d 135.03 ± 0.90c 23.27 ± 0.27c 0.15 ± 0.00a 1.51 ± 0.01a 0.41 ± 0.00bc T2 22.34 ± 0.39a 1.27 ± 0.02ab 77.43 ± 0.70a 42.28 ± 0.24b 250.75 ± c 138.44 ± 0.17b 24.50 ± 0.78bc 0.14 ± 0.00a 1.48 ± 0.00a 0.42 ± 0.002a T3 22.50 ± 0.14a 1.30 ± 0.03ab 77.95 ± 1.33a 43.12 ± 0.10ab 257.99 ± b 141.00 ± 0.37a 25.77 ± 0.34ab 0.14 ± 0.00a 1.52 ± 0.03a 0.40 ± 0.01c T4 22.73 ± 0.29a 1.32 ± 0.02a 79.03 ± 0.54a 43.95 ± 0.34a 285.73 ± a 142.25 ± 0.38a 26.51 ± 0.19a 0.14 ± 0.00a 1.50 ± 0.01a 0.43 ± 0.00a Root stage CK 19.72 ± 0.40b 1.29 ± 0.05a 76.06 ± 0.23c 34.22 ± 0.45d 190.31 ± e 147.99 ± 1.05d 25.67 ± 0.39d 0.13 ± 0.01a 1.50 ± 0.03a 0.42 ± 0.00a T1 20.40 ± 0.15b 1.31 ± 0.05a 76.89 ± 0.89c 35.96 ± 0.26c 230.85 ± d 157.58 ± 0.88c 28.20 ± 0.16c 0.13 ± 0.01a 1.47 ± 0.02a 0.42 ± 0.01a T2 22.56 ± 0.69a 1.36 ± 0.03a 79.05 ± 0.25b 39.21 ± 0.29b 268.77 ± c 160.24 ± 0.35c 28.96 ± 0.48c 0.12 ± 0.01a 1.48 ± 0.00a 0.42 ± 0.01a T3 22.66 ± 0.27a 1.39 ± 0.03a 81.11 ± 0.61a 40.17 ± 0.29b 281.45 ± b 169.65 ± 0.58b 32.31 ± 0.51b 0.12 ± 0.01a 1.49 ± 0.00a 0.41 ± 0.01a T4 22.72 ± 0.18a 1.36 ± 0.02a 81.93 ± 0.90a 41.83 ± 0.62a 307.50 ± a 174.78 ± 1.20a 33.64 ± 0.30a 0.13 ± 0.01a 1.46 ± 0.02a 0.43 ± 0.01a Early nodulation CK 19.84 ± 0.10b 1.19 ± 0.01c 77.32 ± 0.25e 33.51 ± 0.17c 216.47 ± e 162.73 ± 0.26e 28.77 ± 0.12e 0.12 ± 0.01a 1.51 ± 0.03a 0.41 ± 0.00c T1 20.43 ± 0.22b 1.22 ± 0.04bc 79.65 ± 0.56d 34.90 ± 0.11b 232.86 ± d 192.96 ± 0.36d 35.17 ± 0.27d 0.11 ± 0.00a 1.46 ± 0.02a 0.42 ± 0.01ab T2 22.62 ± 0.06a 1.23 ± 0.02abc 84.76 ± 0.77c 38.25 ± 0.74a 278.69 ± c 231.22 ± 0.23c 43.04 ± 0.18c 0.12 ± 0.00a 1.47 ± 0.01a 0.42 ± 0.00bc T3 23.03 ± 0.40a 1.27 ± 0.03ab 90.48 ± 0.78a 38.77 ± 0.30a 291.43 ± b 287.31 ± 0.40a 58.95 ± 0.05a 0.12 ± 0.00a 1.45 ± 0.03a 0.43 ± 0.00ab T4 22.99 ± 0.36a 1.30 ± 0.01a 87.61 ± 0.52b 37.88 ± 0.29a 311.37 ± a 273.36 ± 0.24b 55.52 ± 0.29b 0.11 ± 0.01a 1.45 ± 0.03a 0.43 ± 0.00a Mid nodulation CK 19.47 ± 0.27c 1.08 ± 0.03b 86.34 ± 0.70d 33.28 ± 0.51b 304.66 ± e 140.05 ± 0.72e 27.67 ± 0.34e 0.14 ± 0.01a 1.51 ± 0.02a 0.41 ± 0.01c T1 20.83 ± 0.37b 1.16 ± 0.00a 88.01 ± 0.13c 34.12 ± 0.38b 314.13 ± d 186.78 ± 0.23d 35.08 ± 0.30d 0.14 ± 0.01a 1.47 ± 0.01a 0.42 ± 0.01bc T2 22.76 ± 0.43a 1.17 ± 0.01a 90.53 ± 0.69ab 37.45 ± 0.14a 358.65 ± c 185.72 ± 0.13c 37.15 ± 0.40c 0.13 ± 0.01a 1.47 ± 0.01a 0.43 ± 0.00ab T3 23.66 ± 0.38a 1.20 ± 0.02a 91.36 ± 0.26a 38.19 ± 0.24a 368.88 ± b 242.73 ± 0.37a 53.18 ± 0.24a 0.15 ± 0.01a 1.45 ± 0.01a 0.44 ± 0.00a T4 23.56 ± 0.08a 1.18 ± 0.01a 89.42 ± 0.43bc 37.17 ± 0.20a 391.13 ± a 228.56 ± 0.20b 46.69 ± 0.18b 0.14 ± 0.01a 1.45 ± 0.03a 0.432 ± 0.00ab Harvesting stage CK 19.76 ± 0.25b 1.13 ± 0.05b 82.34 ± 0.55d 29.30 ± 0.30c 286.75 ± c 129.74 ± 0.16d 17.86 ± 0.40d 0.14 ± 0.01a 1.53 ± 0.02a 0.41 ± 0.00d T1 21.00 ± 0.38b 1.16 ± 0.01b 84.84 ± 0.20c 30.90 ± 0.38b 277.07 ± d 144.21 ± 0.85c 22.28 ± 0.22c 0.15 ± 0.00a 1.49 ± 0.00ab 0.42 ± 0.00cd T2 22.77 ± 0.59a 1.31 ± 0.02a 85.42 ± 0.60c 33.71 ± 0.25a 296.16 ± b 158.82 ± 1.02b 25.02 ± 0.22b 0.14 ± 0.01a 1.46 ± 0.02ab 0.43 ± 0.00bc T3 24.26 ± 0.91a 1.38 ± 0.03a 89.65 ± 0.48a 34.61 ± 0.75a 295.86 ± b 170.08 ± 0.99a 29.67 ± 0.19a 0.16 ± 0.01a 1.44 ± 0.02b 0.45 ± 0.01a T4 24.16 ± 0.13a 1.14 ± 0.04a 87.15 ± 0.16b 31.32 ± 0.16b 358.10 ± a 157.40 ± 0.72b 25.88 ± 0.31b 0.15 ± 0.00a 1.43 ± 0.03b 0.44 ± 0.00ab Note: SOM-organic matter; TN-total nitrogen; AN-alkaline nitrogen; AP-rapid phosphorus; AK-rapid potassium; MBC-microbial carbon; MBN-microbial nitrogen; MC-soil water content; SBD-soil bulk density; TP-soil porosity. -MC-soil water content; SBD-soil bulk density; TP-soil porosity. Data are mean ± standard error. Different letters after the data in the same column indicate significant differences between treatments (P < 0.05) 2.2 Effect of fermented biogas slurry returning of tail vegetables on soil enzyme activity 2.2.1 Effect of fermented biogas slurry returning on urease activity As shown in Fig. 1 , the urease activity of the vegetables increased with the application of biogas slurry, and the increase of urease activity also increased with the increase in biogas slurry returned to the field. Specifically, T1, T2, T3 and T4 increased by 5.89%, 3.49%, 4.96%, and 2.41%, respectively, under biogas slurry application. T1, T2, T3 and T4 were significantly higher than CK, but there was no significant difference between T1 and T4, T2 and T3 treatments. At the rosette stage, T1, T2, T3 and T4 increased 4.26%, 5.57%, 5.63% and 5.14%, respectively, with no significant difference between T1 and CK. Treatments T2, T3 and T4 were significantly higher than CK, but there was no significant difference between treatments T2, T3 and T4. Compared to CK, T1, T2, T3, and T4 increased by 8.18%, 9.78%, 12.71%, 1 and 11.02%, respectively, with no significant difference between treatments. T1, T2, T3 and T4 increased by 8.09%, 11.99%, 17.30%, 12.60%, 7.33%, 13.61%, 21.83% and 14.11%, respectively. Urease activity was significantly higher under T1, T2, T3 and T4 treatments than CK, but there was no significant difference between T2 and T4 treatments. Compared with CK, the urease activity increases of T1, T2, T3 and T4 were 4.26%~8.18%、3.49%~13.61%、4.96%~21.83%、5.14%~14.11% respectively. 2.2.2 Effect of fermented biogas slurry returning of tail vegetables on soil sucrase activity Soil sucrase is a key enzyme that is closely related to soil organic matter and aggregate surface area, and is considered as one of the important measures of soil fertility level and biological activity. Figure 2 shows that with the increase of sucrase activity in the growth period, the sucrase activity of each growth cycle basically showed a positive growth trend with the increase of biogas slurry returned to the field. T1, T2, T3 and T4 increased 10.14%, 10.79%, 11.60%, 11.70% at seedling 1, and the differences between T1, T2, T3 and T4 were not significant, but all were significantly higher than those of CK. Rosette stage T1, T2, T3, T4 increased 12.21%, 16.20%, 17.20%, 22.29%, T1, T2, T3, T4 significantly higher than CK. The growth of T1,71%, T2%, T3, T4,21.19%, T1,11.93%, 11.63%, 18.15%, 19.90% and 9.22%, T1, T2, T3 and T4 were significantly higher than CK, but there was no significant difference between T 1 and T4, T2 and T3 treatments. T1, T2, T3, T4 increased 10.60%, 13.79%, 17.38%, 8.78%, T1, T2, T3, T4 were significantly higher than CK, and there was no significant difference between T1 and T4 treatments. Compared with CK treatment, the increases of T1, T2, T3 and T4 were 8.71%~12.21%, 13.79%~20.19%, 11.60%~21.97%, 8.78%~22.29%. 2.2.3 Effect of fermented biogas slurry returning of tail vegetables on alkaline phosphatase activity It can be seen from Fig. 3 that that the alkaline phosphatase activity of tail cabbage increased under the fermented biogas slurry treatment in all growth cycles except the harvest period, and that the range of increase increased with the increase in biogas slurry return except at T4. Under biogas slurry treatments, T1, T2, T3 and T4 increased by 4.23%, 5.37%, 5.72% and 4.76% at seedling stage respectively. There were no significant differences between the T1, T2, T3 and T4 treatments, but they were significantly higher than the CK. T1, T2, T3 and T4 increased by 2.85%, 5.77%, 8.16%, 3.57% and 1.95%, 5.38%, 7.96% and 2.56%, respectively, whereas T1, T2, T3 and T4 were significantly higher than those of CK and there was no significant difference between treatments T1 and T4. T1, T2, T3 and T4 increased by 2.36%, 5.89%, 6.60% and 4.40% in the middle stage of balling, and T1, T2, T3 and T4 were significantly higher than those of CK, and there was no significant difference between treatments T2 and T3. T1, T2, T3 and T4 increased by 8.72%, 9.87%, 10.38% and 5.88% at harvest, and T1, T2, T3 and T4 were significantly higher than those of CK, and there was no significant difference between treatments T1 and T2. Compared with CK, the increases in T1, T2, T3 and T4 were 1.95%~8.72%, 5.37%~9.87%, 5.72%~10.38% and 2.56%~5.88%, respectively. 2.2.4 Effect of fermented biogas slurry returning of tail vegetables on catalase activity Catalase prevents the accumulation of peroxides in the soil by breaking them down in the soil and preventing them from accumulating in living organisms, thereby avoiding damage to crops. It can be seen from Fig. 4 that the total catalase activity did not change significantly as the growth period of baby cabbage progressed, but the soil catalase activity showed a decreasing trend with the increase of biogas slurry application to the field in each growth cycle. At the seedling stage, T1, T2, T3 and T4 catalase activity decreased by 1.68%, 3.91%, 4.29% and 6.25% respectively, with no significant difference between T1 and CK, and T2, T3 and T4 were significantly lower than CK. T1, T2, T3 and T4 decreased by 2.28%, 3.92%, 5.75% and 7.94% at rosette stage, T1, T2, T3 and T4 were significantly lower than those in CK, and there were no significant differences between T1 and T2, T3 and T4 treatments. T1, T2, T3 and T4 decreased by 2.72%, 4.44%, 5.25% and 7.43%, respectively, in the early stage of ball formation, while T1, T2, T3 and T4 were significantly lower than those of CK, with no significant difference between treatments T2 and T3. T1, T2, T3 and T4 decreased by 2.24%, 4.22%, 5.47% and 7.80%, respectively in the middle stage of balling, and T1, T2, T3 and T4 were significantly lower than CK, and there was no significant difference between treatments T1, T2 and T3. T1, T2, T3 and T4 decreased by 2.4%, 2.96%, 4.25% and 6.28% at harvest. T1, T2, T3 and T4 were significantly lower than CK, and there was no significant difference between T1, T2 and T3 treatments. During the whole growth period of baby cabbage, the catalase activity of T1, T2, T3 and T4 decreased by 1.68%~2.72%, 2.96%~4.44%, 4.25%~5.75% and 6.25%~7.94% compared to CK treatment. 2.3 Correlation analysis of soil physicochemical factors and enzyme activity The correlation analysis between soil enzyme activity and physicochemical properties of soil (Fig. 5 ) indicate that there was a significantly positive correlation between soil urease activity and alkaline nitrogen, soil water content, MBC, MBN and quick acting phosphorus (p < 0.05); soil sucrase activity and soil organic matter, alkaline nitrogen, quick phosphorus, MBC, MBN, total nitrogen, soil moisture content and soil bulk density showed a significant positive correlation (p < 0.05); There was a significant positive relationship between alkaline phosphatase activity and alkaline hydrolysis nitrogen, MBC, MBN, organic matter, total nitrogen content and water content (p < 0.05); A significant positive correlation was found between catalase activity and soil rapid phosphorus and total nitrogen content (p < 0.05). 2.4 Comprehensive evaluation of soil fertility under different fertilization treatments The correlation of fertilization treatment with soil physicochemical properties and enzyme activity not only reflects the relationship between soil substances and nutrients in the energy cycle and transformation process, but also emphasizes the important role of soil enzymes as microbial activity indicators in the soil biochemical process[ 19 ]. To evaluate the effects of fertilization on soil fertility (including physicochemical properties and enzyme activities), a principal component-cluster analysis was performed for ten variables including soil organic matter, total nitrogen, alkali hydrolyzable nitrogen, available phosphorus, total nitrogen, MBC, MBN, urease, sucrase, and phosphatase activities at the harvest period (KMO: 0.761, P < 0.005) according to the research protocol of Chen et al [ 20 ]. As shown in Table 4 , one principal component with an eigenvalue greater than 1 was extracted, reflecting 82.28% of the original information (i.e., the cumulative contribution rate of variance was 82.28%), and no original variable was lost. Therefore, it is reliable to use 7 physicochemical indexes and 3 soil enzyme activity indexes selected in this paper to evaluate different fertilization treatments. Table 4 Eigenvalues, variance contributions and factor component shares of principal component analysis ingredient Initial eigenvalue Initial factor loadings sum of squares Principal Component Matrix eigenvalue variance contribution(%) Cumulative contribution (%) eigenvalue Variance contribution (%) Cumulative contribution (%) factor percentage Percentage of variance Cumulative % total Percentage of variance Cumulative % 1 8.229 82.289 82.289 8.2289 82.289 82.289 MBN 0.991 2 0.885 8.847 91.137 MBC 0.990 3 0.261 2.611 93.738 URE 0.986 4 0.210 2.101 95.849 AN 0.921 5 0.197 1.969 97.818 INV 0.907 6 0.129 1.290 99.108 SOM 0.877 7 0.047 0.470 99.578 AP 0.877 8 0.024 0.244 99.822 AK 0.869 9 0.016 0.155 99.977 ALP 0.818 10 0.002 0.023 100.000 TN 0.813 Note: MBN - microbial nitrogen; MBC - microbial carbon; URE - urease activity; AN - alkaline nitrogen removal; INV - sucrase activity; SOM - organic matter; AP -quick-acting phosphorus; AK-quick-acting potassium; ALP-alkaline phosphatase activity; TN-total nitrogen; The extracted principal component weights were calculated based on the raw data and feature values, combined with the data after standardization (eliminating data magnitude and their contribution rate), the successful component score function expression: F = 0.1204 MBN + 0.1203 MBC + 0.1198 urease activity + 0.1119 alkaline nitrogen + 0.10.1102 sucrase activity + 0.1066 organic matter + 0.1066 rapid phosphorus + 0.1056 rapid potassium + 0.0994 phosphatase activity + 0.0988 total nitrogen. The sum of the main component of the composite score and its contribution rate, there is only one principal component in this study, so the comprehensive score Z = FI 82.289%. The comprehensive score was classified as a new index for clustering, and the soil fertility was sorted as T3 > T2 > T4 > T > T1 > CK (as shown in Fig. 6 ) Discussion 3.1 Effects of fertilization on soil physicochemical factors Basic physicochemical factors such as nitrogen, phosphorus, potassium, MBC, MBN and the moisture content of the soil in soil directly reflect the ability of the soil to provide the nutrients needed for crops. Long-term use of chemical fertilizers, coupled with the absorption and elimination of alkali cations by plants, can easily lead to soil acidification, compaction and fixation or loss of nutrients [ 21 ]. Studies have shown that the application of biogas slurry have a tendency to increase the content of soil organic matter, total nitrogen, available phosphorus and other nutrients compared to chemical fertilizers alone, but the excessive application of biogas slurry did not further increase soil nutrients [ 22 – 24 ]. In this study, compared with CK, the contents of soil organic matter, total nitrogen, alkaline hydrolyzable nitrogen, available phosphorus and microbial biomass carbon (nitrogen) were increased by 2.45%~22.97%, 1.29%~24.49%, 1.10%~17.02%, 2.51%~22.23%, 5.6%~76.56% and 9.49%-104.9%, respectively, because the biogas slurry introduced some nutrients [ 25 , 26 ] or some beneficial microorganisms, such as phosphate-solubilizing bacteria, which increases the effectiveness of phosphorus [ 27 ]. As the growth cycle of baby vegetables advances, the organic matter content in the soil under the fermented biogas slurry of tail vegetables returned to the field showed an increasing trend, which is due to the organic matter brought in by the digestate [ 28 ], but with the increase in the amount of tfermented biogas slurry of tail vegetables returned to the field and the passage of time and the effect of the growth of organic matter will be gradually weakened. On the one hand, as the amount of the fermented biogas slurry of tail vegetables returned to the field increased, the possible decomposed substances in the soil increased, and the soil was in a saturated state, so the effect of organic matter growth was weakened by continuing to increase the amount of biogas slurry returned to the field. On the other hand, with the passage of time, the organic matter that is easily decomposed in the soil is gradually degraded, and the remaining organic material is more difficult to decompose, which leads to the slowdown of the decomposition rate of organic matter and limits the growth of organic matter.Soil total nitrogen "S" trend, it is closely related to crop growth characteristics and fertilization strategy, seedling, rosette, baby vegetables small and limited absorption of nitrogen in soil nitrogen accumulation, early, middle, baby vegetable growth of massive consumption of nitrogen in the soil, and harvesting period baby vegetables mainly internal material conversion, reduce the absorption of nitrogen, so the nitrogen in the soil and began to accumulate [ 29 ]. The content of alkaline hydrolyzable nitrogen in the soil first increased and then decreased, which may be related to the fertilization method and the fertilization period. Since there was no fertilization was applied after nitrogen supplementation at the middle stage of balling, the alkaline hydrolyzable nitrogen content decreased at the harvest stage under the loss of crop absorption consumption, nitrogen leaching and volatilization. At each growth stage, the alkaline-hydrolyzable nitrogen content was higher than that of the CK under each fertilization treatment, which may be related to the morphology of the nitrogen brought into the biogas slurry and the ability of the biogas slurry to increase urease activity [ 30 ], which is consistent with the trend that the alkaline-hydrolyzable nitrogen content first increased and then decreased during the growth period of potato by chemical fertilizer combined with organic fertilizer according to Du et al [ 31 ]. The quick-acting phosphorus in the soil showed a decreasing trend with the advancement of the fertility stage of baby cabbage, which may be because the phosphorus fertilizer was applied as the base fertilizer at one time, and the available phosphorus was continuously consumed during the growth period. At each growth stage, the content of available phosphorus in soil under application of biogas slurry was higher than CK, which may be related to the form of phosphorus introduced by biogas slurry (mainly available phosphorus), which was proved by NIYUNGEKOC et al [ 32 ]. Both MBC and MBN in the soil first increased and then decreased. This may be related to fertilization and the external ambient temperature. The Seedling and rosette stage, initial fertilization and temperature increase the number of soil microorganisms, causing the MBC and MBN to increase. High external temperature in the middle knot stage and harvest period, decreased number of soil microorganisms, so both showed a downward trend. With the increasing return of biogas slurry during each growth stage, MBC and MBN were higher than CK with only chemical fertilizer, This may be because the tail vegetables fermented biogas slurry brings in a large number of microorganisms, This is consistent with the conclusion by Chai et al [ 33 ] who revealed that replacing chemical fertilizer studied with biogas slurry in asparagus field can significantly improve the carbon and nitrogen content of soil microorganisms. The present study showed that soil organic matter, total nitrogen, alkaline dissolved nitrogen, quick-acting phosphorus, MBC and MBN content generally increased and then decreased with the increase in the amount of biogas slurry applied to the field from taille vegetable fermentation, which is consistent with the results of Yan et al [ 34 ] who showed that the concentrations of SOM, AN, AP, AK and TN in soil first increased and then decreased with the increase in biogas slurry application. This may be because the excessive application of biogas slurry leads to the accumulation of salt or the introduction of some harmful substances, which suppresses microbial activities, and then affect the decomposition of organic matter and the release of nutrients [ 35 , 36 ]. Combined with this test, the T3 treatment had the best effect in promoting soil fertility. Compared with CK in the same period, organic matter, total nitrogen, alkaline nitrogen, quick phosphorus, and microbial carbon (nitrogen) increased by 13.68%~22.79%, 6.29%~21.83%, 5.81%~17.02%, 144.74% ~ 18.11%, 10.27%~75.56%, 21.26%~104.91%, respectively. 3.2 Effect of fertilization treatments on soil enzyme activities Soil physical and chemical indicators have always played an important role in the assessment of soil quality and fertility, but under the influence of changing environmental conditions and anthropogenic activities, these traditional indicators are no longer able to comprehensively reflect the quality of soil, so that in recent years the enzyme activity of soil has been emphasized as a comprehensive indicator by scientists [ 37 ]. Urease converts nitrogen into ammonia or ammonium nitrogen which can be directly absorbed and utilized by the crop by catalyzing the hydrolysis of urea. Therefore, urease activity is used as an important indicator of the status soil nitrogen supply [ 38 ]. Our results found that the return of biogas slurry can improve urease activity, which may be due to the fact that the fermentation of biogas slurry stimulates the activity of microorganisms and improves the metabolism of soil microorganisms, thus improving enzyme activity [ 39 ]. During the growth period of baby cabbage, the dynamic changes of soil urease are closely correlated with the growth stage of plants. In particular, soil urease and alkaline phosphatase showed the lowest activity at the seedling stage, which may be related to the level of fertilizer demand, soil temperature and seasonal factors. Enzyme activity decreases when the hydrothermal conditions in the soil impair the microbial function of the soil, which is consistent with the findings of Emmert et al [ 40 ]. From the rapid growth of baby cabbage to the middle of the ball, because baby cabbage needs more nutrients, soil microorganisms need to secrete more biological enzymes to transform.When the crop stops growing during the harvesting period, the activity of the enzyme decreases. Sucrase breaks down sucrose into glucose and fructose, which provide direct nutrients for soil microorganisms and plant roots, and its activity reflects soil organic carbon storage and its decomposition process and is an indicator of the level of soil fertility and the degree of soil maturation [ 41 ]. In this experiment, it was found that sucrase activity increased from the seedling stage to the early nodulation stage and decreased at the middle stage of nodulation and harvest, which may be due to temperature and the "slow-fast-slow" growth characteristic of plant growth. At the seedling and rosette stages of baby cabbage, sucrase activity was low because the root system was small, and the biosolids had just been applied, and soil temperature was low. However, with the growth of baby cabbage, the expansion of the root system, the increase in temperature and the accumulation of biosolids, sucrase activity gradually increased and finally peaked in the early nodulation stage, and then led to the decline of sucrase activity in the soil with the reduction of plant growth and excessively high temperatures [ 19 , 42 ]. Sucrase activity increased and then decreased as the amount of biogas slurry increased. Under the replacement of T4 biogas slurry, the sucrase activity was lower than that under the T3 treatment, which is consistent with the results of ZHang et al [ 43 ]. The reason could be that the high concentration of biogas slurry returned to the field contains some substances that inhibit sucrase activity, or that when there are too many organic substances in the biogas slurry, the microorganisms preferentially utilise other carbon sources and reduce the degradation of sucrose, resulting in a decrease in sucrase activity [ 44 ]. Alkaline phosphatase can reflect the phosphorus supply capacity of the soil by hydrolyzing the organic phosphorus compounds in the soil and providing plants with directly available phosphorus [ 8 ]. The present experiment showed that the returning fermented biogas slurry from tail vegetables to the field could significantly increase the soil alkaline phosphatase activity, which could be attributed to the rich organic matter in the biogas slurry, which stimulated microbial metabolic activities and led to an increase in alkaline phosphatase activity. This is consistent with the findings of ZHu et al [ 45 ]. From seedling stage to mid-balling stage of baby cabbage, the alkaline phosphoric acid activity increased as the growth stage of cabbage progressed, which may be due to two reasons; Firstly, the microbial activity and enzyme activity increase with the increases in temperature, and secondly, the pH of biogas slurry itself is high, and the continuous accumulation of biogas slurry in the seedling stage, rosette stage, early stage of balling and middle stage of balling leads to the increase of pH value around the rhizosphere and promotes the increase of alkaline phosphatase activity, while the decrease of alkaline phosphatase activity at harvest stage may be due to the high soil temperature and the decrease of enzyme activity. Previous studies have shown that a large amount of biogas slurry returned to the field increases pH, decreases acidic phosphoric acid activity, and increases alkaline phosphatase activity [ 46 , 47 ].Catalase is commonly found in soil microorganisms and mainly decomposes hydrogen peroxide which is harmful to organisms, protects soil microorganisms and plant roots from oxidative damage, and characterizes the activity of soil oxidation processes and the intensity of soil biochemistry [ 8 ]. In this study, it was found that as the growth period of baby cabbage progressed, there was no significant change in hydrogen peroxide activity under each fertilization treatment, which may be related to the short application cycle of biogas slurry[ 48 ], and in this experiment, which may be related to the abundant active substances in the biogas slurry, which can degrade toxic substances such as peroxide in the rhizosphere and protect the root system to maintain normal physiological function, which was confirmed by the results of Guan et al [ 49 ]. Zhang et al [ 50 ] found that the return of straw significantly increased soil sucrase and urease activities in soil, but had no significant effect on catalase activity. In conclusion, this study showed that the return of fermented biogas slurry from tail vegetables increased the activities of urease, sucrase and alkaline phosphatase in soil, which may be due to the stimulation of the activity of microorganisms and the improvement of the metabolism of soil microorganisms, thereby improving enzyme activity[ 39 ]. This is in line with previous studies showing that biogas slurry has a positive correlation with the activities of sucrase and alkaline phosphatase [ 45 , 51 ]. In this study, the activities of urease, sucrase and alkaline phosphatase were lower under T4 (biogas slurry) treatment than under T3, suggesting that the biogas slurry should be returned to the field in moderation. This could be due to salt accumulation stress caused by excessive biogas slurry application, which limited root system development, inhibited the number and activity of soil microorganisms, and directly affected enzyme activity [ 30 , 52 ]. Studies have shown that the appropriate application of nitrogen, phosphorus and potassium fertilizers under the biogas slurry rate or by reasonably controlling the carbon to nitrogen ratio in the soil can significantly improve the activity of soil enzymes [ 53 ], so returning biogas slurry to the field is an important way to improve soil fertility from the perspective of soil enzymes. It has also been shown that the combination of nitrogen, phosphorus and potassium fertilizers at appropriate biogas slurry levels or by reasonably regulating the carbon and nitrogen ratio in the soil can significantly improve the activity of soil enzymes [ 54 , 55 ], and from the perspective of soil enzymes, returning methane gas from taille fermentation to the field is an important way to improve soil fertility. 3.3 Effect of correlation between soil physicochemical factors and enzyme activities under fertilization treatments The availability of nutrients in the soil is strongly correlated with the activity of soil enzymes, which could be due to a positive feedback between the two [ 56 ]. Significant positive correlations between soil urease activity and alkali dissolved nitrogen, soil water content, MBC, MBN and fast-acting phosphorus indicate the importance of urease activity in indicating soil N availability and soil microbial vigor. Yuan et al [ 51 ]. found a positive correlation between soil nutrients and microbial communities because microorganisms supply soil with C and N and thus improve soil fertility, and the reason analyzed may be that urease is produced by microorganisms and is involved in the degradation of urea. MBC and MBN are indicators of microbial abundance and activity in the soil, microorganisms obtain and release nutrients such as carbon and nitrogen through the decomposition of organic matter and substrates such as urea, which can provide more substrates for the urease reaction, thus increasing urease activity. In addition, appropriate soil moisture content can create suitable environmental conditions for microbial growth and metabolism, which can increase urease activity. Sucrase activity in soil was significantly and positively correlated with soil organic matter, alkaline dissolved nitrogen, quick-acting phosphorus, MBC, MBN, total nitrogen, soil water content and soil bulk density, indicating that sucrase activity is closely related to the nutrient status and structure. Organic matter is the main substrate for sucrase, and increasing its content can promote higher sucrase activity. Higher levels of alkaline dissolved nitrogen and fast-acting phosphorus may have provided microorganisms and sucrase with more nutrients and thus promoted sucrase activity; sucrase is produced by microbial metabolism and is involved in the degradation of sucrose; microorganisms obtain carbon and nitrogen sources by decomposing organic matter and substrates; higher MBC, MBN and total nitrogen in the soil are available to microorganisms and sucrase, which promotes sucrase activity; suitable soil conditions such as soil temperature, water content and lower soil bulk density favor the activities of microorganisms and enzymes [ 57 ]. Soil alkaline phosphatase activity showed significant positive correlations with alkaline dissolved nitrogen, MBC, MBN, organic matter, total nitrogen and water content, suggesting that alkaline phosphatase effectively controls the degree of soil fertility and the moisture status of the soil. Alkaline phosphatase is produced by microbial metabolism and is an enzyme involved in the mineralization process of organophosphate. MBC and MBN characterize microbial abundance, higher levels of organic matter, total nitrogen and alkaline dissolved nitrogen can provide more substrate for alkaline phosphatase, which promotes enzyme activity; higher soil water content can provide suitable environmental conditions to promote microbial growth and metabolism, which in turn increases enzyme activity [ 58 ]. Catalase activity showed a significant positive correlation with fast phosphorus and total nitrogen content in soil. Catalase plays an important role in redox reactions. The content of fast-acting phosphorus and total nitrogen may affect the redox environment of the soil, and a suitable redox environment has an important influence on catalase activity. Higher levels of fast-acting phosphorus and total nitrogen may help to maintain a suitable redox environment, which promotes catalase activity. 3.4 Effect of fertilization treatments on overall soil fertility The physical and chemical properties of the soil can affect the enzyme activity in the soil, while the enzyme activity reflects the biological activity and the ability to provide substances and nutrients in the soil. Soil enzyme activity and soil physical and chemical properties were calculated by downscaling and weighting to obtain a composite score, and fertilizer treatments were evaluated accordingly. In this study, as the amount of biogas slurry returned to the field increase, the comprehensive score of each treatment first increased and then decreased, indicating that the return of biogas slurry had a positive effect on soil fertility, which is consistent with the results of Wang et al [ 59 ]. The score of T3 treatment was the highest in fertilization treatment, and the score decreased in the T4 treatment, indicating that an appropriate amount of biogas slurry should be returned to the field. An inappropriate amount of biogas slurry returned to the field will lead to an imbalance of various physical and chemical indices and enzyme activities, and excessive or low application of biogas slurry would lead to the imbalance of soil nutrients, microbial activities and enzyme activities, resulting in poor soil comprehensive fertility. Chai et al [ 33 ] showed that the substitution of chemical fertilizer with biogas slurry by 50% could significantly increase the content of soil organic matter and available potassium, but have no significant effect on total nitrogen, alkali hydrolyzable nitrogen and available phosphorus, and the substitution of chemical fertilizer with biogas slurry by 100% increased sucrase activity and urease activity, but decreased phosphatase. ZHao et al [ 13 ] showed that the application fermented biogas slurry of taille vegetables could significantly maintain the production yield of cauliflower and improve the quality of cauliflower, but the excessive application could greatly reduce the utilization rate of nitrogen. Conclusion (1)The return fermented biogas slurry of taille vegetables to the field significantly increased the content of soil organic matter, total nitrogen, alkaline dissolved nitrogen, quick-acting phosphorus, quick-acting potassium, microbial carbon and microbial nitrogen, and the soil porosity tended to increase, the soil bulk density tended to decrease and had a relatively small effect on soil moisture content. The increase of organic matter, total nitrogen, alkaline-hydrolyzable nitrogen, available phosphorus, available potassium, microbial biomass carbon and microbial biomass nitrogen under T3 (246m 3 ·hm − 2 taille vegetables fermented biogas slurry + 44kg·hm − 2 chemical nitrogen) was 13.66 ~ 21.48%, 6.29 ~ 21.83%, 5.81 ~ 17.03%, 4.74 ~ 18.11%, 3.18 ~ 47.89%, 10.27 ~ 76.58% and 21.27 ~ 104.94%, respectively. (2)The return of fermented biogas slurry of tail vegetables to the field significantly increased the activities of the soil enzymes urease, sucrase and alkaline phosphatase, but had little effect on catalase activity, and there was no significant difference. After biogas slurry application, the activities of soil enzymes such as urease, sucrase and alkaline phosphatase increased by 2.41–21.83%, 8.71%~22.29% and 1.95%~10.38%, respectively, among which T3 treatment increased by 0.96–21.83%, 11.7%~21.97% and 5.72%~10.38%. (3)The cluster analysis was carried out with the composite score value of the principal components as the new index, and the soil fertility under fertilization treatments was in the order of T3>T2>T4>T1>CK, and the T3 treatment had the highest composite score and the best fertility. Considering the comprehensive effects of fermented biogas slurry of tail vegetables fertilization treatments on soil physicochemical properties, soil microbial function and baby cabbage production performance, the ratio of 75% biogas slurry nitrogen and 25% chemical nitrogen in fertilization treatment had the best effect. Declarations Author Contribution Author Contributions: Conceptualization, S.Z.Y. and R.C.; methodology, B.L. and S.Z.Y.; software, J.H.; validation, S.Z.Y. and B.L.; resources, S.Z.Y and R.C.; data curation, J.H.; writing—original draft preparation, S.Z.Y.; writing—review and editing, R.C., and S.Z.Y.; supervision, R.C.; project administration, S.Z.Y.; funding acquisition, R.C. 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Journal of Anhui Agricultural Sciences 2012. Shubiao, W. Effect of Biogas Slurry on Yield Increase,Quality Improvement,Water and Soil Environment. Transactions of the Chinese Society for Agricultural Machinery 2013. Bian, B.; Lin, C.; Lv, L. Health risk assessment of heavy metals in soil-plant system amended with biogas slurry in Taihu basin, China. Environmental Science & Pollution Research 2016. Xu, L.; Yi, M.; Yi, H.; Guo, E.; Zhang, A. Manure and mineral fertilization change enzyme activity and bacterial community in millet rhizosphere soils. World Journal of Microbiology and Biotechnology 2017, 34 , 8, doi: 10.1007/s11274-017-2394-3 . Liang, W.; Wu, Z.; Cheng, S.; Zhou, Q.; Hu, H. Roles of substrate microorganisms and urease activities in wastewater purification in a constructed wetland system. Ecol. Eng. 2003, 21 , 191–195, doi: 10.1016/j.ecoleng.2003.11.002 . Iovieno, P.; Morra, L.; Leone, A.; Pagano, L.; Alfani, A. Effect of organic and mineral fertilizers on soil respiration and enzyme activities of two Mediterranean horticultural soils. Biol. Fertil. Soils 2009, 45 , 555–561, doi: 10.1007/s00374-009-0365-z . Emmert, E.A.B.; Geleta, S.B.; Rose, C.M.; Seho-Ahiable, G.E.; Briand, C.H. Effect of land use changes on soil microbial enzymatic activity and soil microbial community composition on Maryland's Eastern Shore. Appl. Soil Ecol. 2020, 161 , 103824. Sardans, J.; Peñuelas, J.; Estiarte, M. Changes in soil enzymes related to C and N cycle and in soil C and N content under prolonged warming and drought in a Mediterranean shrubland. Appl. Soil Ecol. 2008, 39 , 223–235, doi: 10.1016/j.apsoil.2007.12.011 . Zheng, W.; Dong, H.; Wang, Z.; Tao, Y. Effect of Straw Returning and Nitrogen Application Rate on Soil Enzymatic Activities. Agric. Res. 2023, 12 , 163–171, doi: 10.1007/s40003-022-00638-3 . Xing-Yi, Z.; Qiang, C.; Yuan, C.; Shuang, L.; Xu-Feng, L.I.; Hao, L.I. Influences of No-Tillage on Soil and Crop Performance in the North Cool Region of Northeast China. Scientia Agricultura Sinica 2013. Zimmerman, A.R.; Gao, B.; Ahn, M. Positive and negative carbon mineralization priming effects among a variety of biochar-amended soils. Soil Biology and Biochemistry 2011, 43 , 1169–1179, doi: https://doi.org/10.1016/j.soilbio.2011.02.005 . Zhu, F.R.; Li, J.H.; Azeem, M.; Qu, W.; Qasim, M.; Yang, S.J. Improvement of yield and quality of chinese cabbage(Brassica rapa pekinensis L.) by augmenting soil fertility,nutrient status,and microbial activity with biogas slurry application. Appl. Ecol. Environ. Res. 2022, 20 , 4985–4997, doi: 10.15666/aeer/2006_49854997 . Peoples, M.B.; Herridge, D.F.; Ladha, J.K. Biological nitrogen fixation: An efficient source of nitrogen for sustainable agricultural production? Springer Netherlands 1995. Dick, W.A.; Cheng, L.; Wang, P. Soil acid and alkaline phosphatase activity as pH adjustment indicators. Soil Biology and Biochemistry 2000, 32 , 1915–1919, doi: https://doi.org/10.1016/S0038-0717(00)00166-8 . Pu, S.H.; Huang, P.; Liu, W.; Yang, S.Q. Study on the Effects of Biogas Slurry Application on Soil Phosphate and Catalase Activity. Advanced Materials Research 2014, 955–959 , 3625–3629, doi: 10.4028/www.scientific.net/AMR.955-959.3625 . Guan T, F.W.W.H. Effect of topdressing biogas slurry on biological activity of rhizosphere soil of winter wheat. Journal of Triticeae Crops 2010, 30 , 721–726. Zhang, J.; Bo, G.; Zhang, Z.; Kong, F.; Wang, Y.; Shen, G. Effects of Straw Incorporation on Soil Nutrients, Enzymes, and Aggregate Stability in Tobacco Fields of China. Sustainability 2016, 8 , 710, doi: 10.3390/su8080710 . Li, Y.; Chang, S.X.; Tian, L.; Zhang, Q. Conservation agriculture practices increase soil microbial biomass carbon and nitrogen in agricultural soils: A global meta-analysis. Soil Biology and Biochemistry 2018, 121 , 50–58, doi: https://doi.org/10.1016/j.soilbio.2018.02.024 . Daffonchio, D.; Hirt, H.; Berg, G. Plant-Microbe Interactions and Water Management in Arid and Saline Soils. Springer International Publishing 2015. Wittmann, C.; Kähkönen, M.A.; Ilvesniemi, H.; Kurola, J.; Salkinoja-Salonen, M.S. Areal activities and stratification of hydrolytic enzymes involved in the biochemical cycles of carbon, nitrogen, sulphur and phosphorus in podsolized boreal forest soils. Soil Biology and Biochemistry 2004, 36 , 425–433, doi: https://doi.org/10.1016/j.soilbio.2003.10.019 . Nayak, D.R.; Babu, Y.J.; Adhya, T.K. Long-term application of compost influences microbial biomass and enzyme activities in a tropical Aeric Endoaquept planted to rice under flooded condition. Soil Biology and Biochemistry 2007, 39 , 1897–1906, doi: https://doi.org/10.1016/j.soilbio.2007.02.003 . Hu, G.; Ma, X.; Li, X.; Wang, H. Evaluation of organic substitution based on vegetable yield and soil fertility. Environmental Pollutants & Bioavailability 2022, 34 , 162–170, doi: 10.1080/26395940.2022.2064335 . Ma, Y.; Fu, S.; Zhang, X.; Zhao, K.; Chen, H.Y.H. Intercropping improves soil nutrient availability, soil enzyme activity and tea quantity and quality. Appl. Soil Ecol. 2017, 119 , 171–178, doi: 10.1016/j.apsoil.2017.06.028 . Wallenstein, M.D.; Mcmahon, S.K.; Schimel, J.P. Seasonal variation in enzyme activities and temperature sensitivities in Arctic tundra soils. Glob. Change Biol. 2009, 15 , 1631–1639, doi: 10.1111/j.1365-2486.2008.01819.x . Boerner, R.E.J.; Brinkman, J.A.; Smith, A. Seasonal variations in enzyme activity and organic carbon in soil of a burned and unburned hardwood forest. Soil Biology and Biochemistry 2005, 37 , 1419–1426, doi: https://doi.org/10.1016/j.soilbio.2004.12.012 . Wang, Y.; Shen, F.; Liu, R.; Wu, L. Effects of anaerobic fermentation residue of biogas production on the yield and quality of Chinese cabbage and nutrient accumulations in soil. Int. J. Glob. Energy Issue 2008, 29 , 284–293. 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-4333390","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":299549822,"identity":"52bb05bf-a6f0-416b-8999-34ddbf5c0263","order_by":0,"name":"Shuzhi Yue","email":"","orcid":"","institution":"Gansu Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Shuzhi","middleName":"","lastName":"Yue","suffix":""},{"id":299549823,"identity":"dd98af78-de59-4efd-80f7-41b55c6bcecf","order_by":1,"name":"Bian Liu","email":"","orcid":"","institution":"Gansu Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Bian","middleName":"","lastName":"Liu","suffix":""},{"id":299549825,"identity":"24662b7f-0f03-40e2-84a1-46886f51ec70","order_by":2,"name":"Huang Jie","email":"","orcid":"","institution":"Gansu Agricultural University","correspondingAuthor":false,"prefix":"","firstName":"Huang","middleName":"","lastName":"Jie","suffix":""},{"id":299549828,"identity":"5b60149f-90ee-4422-b274-969199a13760","order_by":3,"name":"Run Chu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAApklEQVRIiWNgGAWjYDACCTBZI8fG3nyAJC3HjPl4jiWQpIU5cZ5EjgJxOvhn95h95t3Blt7GkMPA8KNiGxGW3DljPJv3jExuG8PZA4w9Z24T1mIgkWPMzNvGltvG2JfAzNhGvBbmdDZmHgPStCSwsRGrReJGWjHj3LZjhm08bAkHifIL/4zkzQxv22rk5ec/PvjgRwURWlDAARLVj4JRMApGwSjABQCpdTLCQx9JJwAAAABJRU5ErkJggg==","orcid":"","institution":"Gansu Agricultural University","correspondingAuthor":true,"prefix":"","firstName":"Run","middleName":"","lastName":"Chu","suffix":""}],"badges":[],"createdAt":"2024-04-27 09:40:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4333390/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4333390/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":56145567,"identity":"fe90b417-1361-4cc8-9ad6-1ca612de099f","added_by":"auto","created_at":"2024-05-09 05:37:02","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":75329,"visible":true,"origin":"","legend":"\u003cp\u003eResponse of soil urease activity to fertilization treatments\u003c/p\u003e\n\u003cp\u003eNote:Different letters indicate significant differences between treatments (P\u0026lt;0.05).\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4333390/v1/73844c5779434f21214f87f3.jpeg"},{"id":56146151,"identity":"d0b62513-f7cf-4b50-b360-810a59842ad3","added_by":"auto","created_at":"2024-05-09 05:53:03","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":74967,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eResponse of soil sucrase activity to fertilization treatments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNote:Different letters indicate significant differences between treatments (P\u0026lt;0.05).\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4333390/v1/412e62dc8b0eae4299431d68.jpeg"},{"id":56145842,"identity":"c2e5afa8-9688-4830-aec4-2beba4900773","added_by":"auto","created_at":"2024-05-09 05:45:02","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":73647,"visible":true,"origin":"","legend":"\u003cp\u003eResponse of soil alkaline phosphatase activity to fertilization treatments\u003c/p\u003e\n\u003cp\u003eNote:Different letters indicate significant differences between treatments (P\u0026lt;0.05).\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4333390/v1/318f3864f800fcddf409236d.jpeg"},{"id":56145137,"identity":"c5993278-8ec4-4e63-8214-32a39220e1b7","added_by":"auto","created_at":"2024-05-09 05:29:02","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":67210,"visible":true,"origin":"","legend":"\u003cp\u003eResponse of soil catalase activity to fertilization treatments\u003c/p\u003e\n\u003cp\u003eNote:Different letters indicate significant differences between treatments (P\u0026lt;0.05).\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4333390/v1/f70cc5c1e1f3d286dbec41db.jpeg"},{"id":56146483,"identity":"f3282b0b-24ed-4b8d-98d3-155df54e5f98","added_by":"auto","created_at":"2024-05-09 06:01:03","extension":"jpeg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":46740,"visible":true,"origin":"","legend":"\u003cp\u003eComprehensive scores of soil fertility under\u003c/p\u003e\n\u003cp\u003eNote:Different letters indicate significant differences between treatments (P\u0026lt;0.05).\u003c/p\u003e","description":"","filename":"floatimage6.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-4333390/v1/d75fef6b27ab56ff06a8f554.jpeg"},{"id":65561343,"identity":"bfe0f30f-0f26-4762-b6dd-50950d68eee1","added_by":"auto","created_at":"2024-09-30 04:01:39","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1391463,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4333390/v1/7547eeb7-bb42-4190-b509-77bca181dae8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effects of fermented biogas slurry returning of tail vegetables on soil enzyme activity and fertility","fulltext":[{"header":"Introduction","content":"\u003cp\u003eSoil fertility is the cornerstone of excellent crop growth and germplasm characteristics, and it has received more and more attention. The application of chemical fertilizers is a double-edged sword; rational application can increase crop yields, while excessive application damages the ecological environment and affect crop yields. At present, the amount of chemical fertilizer used in China\u0026apos;s agricultural production remains high, and the output of grain per unit of chemical fertilizer and the quality of agricultural products are declining year by year[1]. In production, producers only pay attention to chemical fertilizers, ignore the relationship between soil physical and chemical factors, soil enzyme activities and soil structure, and over rely on chemical fertilizers, which leads to a series of problems such as soil acidification, compaction, attenuation of enzyme activity, crop yield reduction and loss of soil quality [2,3]. Soil enzymes originate from the metabolism of soil plants, animals, plants and microorganisms [4], mark the dynamics of soil development and evolution and are one of the most important indicators for assessing soil fertility [5].Urease activity reflects the soil nitrogen status [6], phosphatase activity reflects the amount of phosphorus that can be absorbed and utilized by plants [7],catalase activity reflects the ability of roots to eliminate peroxide toxicity [8] and sucrase activity reflects the level of energy and carbon sources provided by soil for crop growth [9].\u003c/p\u003e\n\u003cp\u003ePlateau summer vegetables are a specialty industry in Gansu Province, with the area under vegetable cultivation increasing by 19,000 hm2 and production increasing by 4.9% by 2022 compared to the previous year[10]. Tail vegetables are waste products generated during the production and processing of vegetables, and are usually accumulated as household waste. Vegetable wastes have high moisture content and if they are piled indiscriminately, they can easily rot, breed mosquitoes and flies, spread germs [11,12] and even lead to clogging of water channels [13]. In addition, the liquid leaking from the accumulation of vegetable wastes can flow into the river, causing water pollution problems. The results showed that the contents of total nitrogen, total phosphorus, and total potassium and C/N were 1.96%~5.39%, 0.35%~1.82%, 0.80%~5.42%, and 6.70~20.35, respectively in tail vegetables, which had high fertilizer utilization value [14],and unreasonable disposal would not only pollute the environment, but also cause waste of resources[13].The remaining liquid (biogas slurry) generated from the anaerobic fermentation of tail vegetables can be returned to the field as fertilizer[15,16], which not only enables the recycling of tail vegetable resources, but also reduces environmental risks and planting costs. This approach is in line with China\u0026apos;s development requirements to promote green and circular agriculture.\u003c/p\u003e\n\u003cp\u003eAt present, there have been a large number of studies on fertilization with biogas slurry, and the results show that the application of biogas slurry can improve the physical and chemical properties of the soil and increase yield and quality of crops. However, the existing studies mainly focus on biogas slurry from livestock and poultry manure biogas slurry, and there are relatively few studies on the utilization of biogas slurry from fermented tail vegetables. However, the efficient use of tail vegetable waste is of great value to limit the expansion of vegetable production areas. The purpose of this study was to analyze the effect mechanism of biogas slurry application on the physicochemical properties of soil and enzyme activities in the process of cultivating baby cabbage in the field. Based on the correlation between the two factors, principal component-cluster analysis will be used to evaluate the impact of biogas slurry returning on soil fertility by using the comprehensive score as a new evaluation index. The purpose of this study is to provide a theoretical basis for the appropriate dosage of fermented biogas slurry of tail vegetables to return to the field and to provide theoretical support for the treatment of tail vegetables in vegetable cultivation areas.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003e1.1 Overview of the test site\u003c/h2\u003e \u003cp\u003eThe trial was conducted from May to July 2023 at Yuansheng Agriculture and Animal Husbandry Co. Ltd. (38\u0026deg;27\u0026prime;N, 102\u0026deg;09\u0026prime;E), Yongchang County, Gansu Province. The area is characterized by a temperate, arid climate with a large temperature difference between day and night. The average effective accumulated temperature (\u0026ge;\u0026thinsp;10\u0026deg;C) is 2011\u0026deg;C, the frost-free period is about 134 days, the average annual temperature is 4.8\u0026deg;C, the average annual precipitation is 185 mm, and the total annual evaporation is 2000.6 mm. The properties of the tested soil are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\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\u003ePhysical and chemical properties of test soil\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003ecomponent\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003epH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSO(g\u0026middot; kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTN(g\u0026middot; kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAN(g\u0026middot; kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eTP(g\u0026middot; kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eAP(g\u0026middot; kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eAK(g\u0026middot; kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003econtent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e22.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.072\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.196\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.029\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e20.49\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"8\"\u003eNote:pH-pH;SOM-organic matter;TN-total nitrogen;AN-alkaline nitrogen;TP-total phosphorus;AP-quick-acting phosphorus; AK-quick-acting potassium.\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e1.2 Test Materials\u003c/h2\u003e \u003cp\u003eThe test crop was baby cabbage with a growth period of about 60 days, a plant height of about 20 cm and a ball diameter of about 10 cm. The organic matter in the tested biogas slurry was 16.271g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, total nitrogen 0.532 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, total phosphorus 0.028 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, total potassium 1.99 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and the pH was 7.35. The tested fertilizers included urea (46% nitrogen), superphosphate (18% P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e) and potassium sulfate (50% K\u003csub\u003e2\u003c/sub\u003eO).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e1.3 Design of Experiments\u003c/h2\u003e \u003cp\u003eIn the experiment, an open-field direct mulching drip irrigation system was used. The area of the plot is 20 m2 (6.45\u0026times;3.1 m), the row spacing of baby cabbage is 25\u0026times;30 cm, and 125,000 plants are planted per hectare. The design principle of the application rate of biogas slurry was to meet the nitrogen demand of baby cabbage. The application rate was calculated according to the nitrogen content in the biogas slurry to ensure that each fertilization treatment is carried out under isonitrogen conditions. It was calculated that the potassium requirement was met in the case of nitrogen requirement, but the phosphorus was insufficient, and a one-time application of superphosphate as a base fertilizer was required. According to the planting experience of local vegetable farmers, baby cabbage requires 174 kg of pure nitrogen, 180 kg of pure phosphorus and 108 kg of pure potassium per hectare. Five isonitrogen fertilization treatments were established: CK (100% chemical nitrogen), T1 (25% biogas slurry nitrogen\u0026thinsp;+\u0026thinsp;75% chemical nitrogen), T2 (50% biogas slurry nitrogen\u0026thinsp;+\u0026thinsp;50% chemical nitrogen), T3 (75% biogas slurry nitrogen\u0026thinsp;+\u0026thinsp;25% chemical nitrogen) and T4 (100% biogas liquid nitrogen) (see Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e for details). Each treatment consisted of three replicates, randomly arranged and surrounded by guard rows. According to the local fertilization experience, the amount of fertilizer applied before sowing (May 28) was 17% of the total amount (calculated as nitrogen fertilizer), 45% at seedling stage (June 12), 14% at rosette stage (June 23), 10% at the early stage of balling (July 1), and 14% at the middle stage of balling (July 11). At the same time, in addition to the irrigation, the water introduced by the biogas slurry was removed during the irrigation process, and the insufficient part was compensated with clean water to ensure that the irrigation amount of the experimental plot was consistent. Field management and other farming activities in the experiment were managed in a unified manner.\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\u003eInput of biogas slurry to replace nitrogen fertilizer\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" 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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTreatment\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNitrogen supply from biogas slurry( kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNitrogen supply fromchemical fertilizers( kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTotal nitrogen application rate\u003c/p\u003e \u003cp\u003e( kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCK\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e174\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e174\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e131\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e174\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e174\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e130\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e174\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e174\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e174\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 \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e1.4 Sample collection and analysis methods\u003c/h2\u003e \u003cp\u003eSoil samples were collected at the seedling stage (June 18), rosette stage (June 29), early balling stage (July 7), mid-balling stage (July 17) and harvest stage (August 1). The \u0026ldquo;S\u0026rdquo; type 5-point sampling method was used to collect soil samples from 0\u0026ndash;20 cm soil layer, mixed evenly, and about 500g of soil samples were taken and divided into two parts. One sample was air-dried, ground, and sieved through a 2 mm and a 0.15 mm sieve for later use. The other fresh soil samples were stored in a freezer at 4\u0026deg;C for the determination of soil enzyme activity, with sampling and pretreatment completed within 24 hours.\u003c/p\u003e \u003cp\u003eThe physicochemical properties of the soil were determined according to the method described in Bao [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Soil bulk density, saturated water conductivity and total porosity were determined by the ring knife method. Potassium dichromate-external heating method was used to determine soil organic matter, whiles alkali hydrolysis diffusion method was used to determine alkali hydrolyzable nitrogen. Molybdenum-antimony resistance indicator method and flame photometer method were used to determine available phosphorus and available potassium respectively. The soil enzyme activity was determined according to the method of Guan et al[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Urease activity was determined by phenol-sodium hypochlorite colorimetric method, sucrase activity by 3,5-dinitrosalicylic acid colorimetric method, alkaline phosphatase activity by benzophthenic acid disodium phosphate colorimetric method, and catalase activity by potassium permanganate titration. The microbial biomass carbon was analyzed by chloroform fumigation-leaching[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e], and TOC instrumental analysis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e1.5 Data processing and statistical analysis\u003c/h2\u003e \u003cp\u003eThe experimental data were organized using Microsoft Excel 2010, and one-way ANOVA, correlation analysis (Pearson's index was used for size) and principal component analysis were performed using SPSS 26.0 (SPSS Inc., Chicago, IL, USA) statistical analysis software, and significant analysis of differences between treatments was performed using Duncan's new complex polarity method with a significance level of P\u0026thinsp;\u0026lt;\u0026thinsp;0.05. Charts and graphs were generated by SPSS 26.0 and Origin 2021 software, respectively.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and Analysis","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1 Effect of biogas slurry returning on soil physicochemical factors\u003c/h2\u003e\n\u003cp\u003eIt can be seen from Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e that biogas slurry application increased the contents of organic matter, total nitrogen, alkali hydrolyzable nitrogen, available phosphorus, available potassium and microbial biomass carbon/nitrogen (MBC/MBN), decreased the soil bulk density, and increased the total porosity. There was no significant difference in the soil moisture content among the treatments. Soil organic matter was increased in all growth cycles under the biogas slurry treatments, and the increase basically showed a trend of increasing with the increase of biogas application. The highest organic matter content was observed at the harvest stage, which increased by 6.24%, 15.20%, 22.77%, and 22.25% in the T1, T2, T3 and T4 treatments compared to CK, respectively. As the growing season progressed, total nitrogen showed an S-shaped trend of \"increase-decrease-increase\", and the range of change was positively correlated with the amount of biogas slurry returned to the field. Compared with the same period of CK, the total nitrogen content of T1, T2, T3 and T4 increased by 2.46%, 3.83%, 6.29%, 8.20%, 1.29%, 5.17%, 7.50% and 5.43%, respectively, and the total nitrogen in the early and middle stages of balling decreased and increased by 2.65%, 15.93% and 21.83% respectively in T1, T2, T3 and T4 and 24.49%. With the except of the harvest period, soil alkaline hydrolyzable nitrogen increased in all other growth cycles, and the increase was basically positively correlated with the amount of biogas slurry. The lowest soil alkaline dissolved nitrogen content was found at the seedling stage: T1, T2, T3 and T4 were increased by 1.93%, 4.86%, 5.81%, and 3.57%, respectively, compared to the CK treatment. The highest soil alkaline dissolved nitrogen content was found in the middle stage of nodulation: T1, T2, T3, and T4 were increased by 3.03%, 3.74%, 8.88%, and 5.83%, respectively, compared to the CK treatment. In general, the content of available phosphorus and available potassium in the soil decreased as the growth cycle progressed. Soil quick-acting phosphorus and quick-acting potassium contents increased with the increase in the amount of biogas slurry returned to the field in each growth cycle. Quick-acting phosphorus was highest at the seedling stage. Compared to CK, T1, T2, T3 and T4 increased by 4.23%, 15.01%, 17.31% and 19.56%, respectively, and lowest in the harvest stage, compared with CK, T1, T2, T3 and T4 increased by 5.46%, 15.05%, 18.11% and 6.89%, respectively. Quick-acting potassium content was the highest with T1, T2, T3 and T4 increasing by 3.11%, 17.72%, 21.08% and 28.38 compared to the CK. The carbon/nitrogen content of microbial biomass (MBC/MBN) initially increased and then decreased as the growth cycle progressed. At the initial stage of nodulation, the content of MBC and MBN was the highest, and T1, T2, T3 and T4 increased by 18.57%, 42.09%, 76.56%, 67.98% (MBC) and 22.27%, 49.50%, 104.94% and 93.00% (MBN), respectively. MBC content was lowest at the seedling stage with T1, T2, T3, and T4 increasing only by 5.60%, 8.27%, 10.27% respectively whiles MBN content was lowest at the harvest period, with the CK, T1, T2, T3, T4 increasing by 24.77%, 40.13%, 66.16%, 44.95%, respectively. The application of biogas slurry had no significant effect on soil moisture content, but some effects on soil bulk density and porosity. Except at the seedling stage, soil bulk density decreased, and porosity increased. The decrease and increase generally increase with increasing addition of biogas slurry. During the harvest period, the soil bulk density of T1, T2, T3 and T4 decreased by 2.62%, 4.59%, 5.46% and 6.55%, respectively, compared to CK.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab3\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eSoil physicochemical factors under different fertilization treatments\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003ePeriod\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003etreatments\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eSOM(g.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eTN(g.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eA(mg.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eAP(mg.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eAK(mg.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMB(mg.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMBN(mg.kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eMC(%)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eSBD(g.cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e)\u003c/p\u003e\n\u003c/th\u003e\n\u003cth align=\"left\"\u003e\n\u003cp\u003eTP(%)\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"5\" align=\"left\"\u003e\n\u003cp\u003eSeedling stage\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCK\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e19.79\u0026thinsp;\u0026plusmn;\u0026thinsp;0.33b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e72.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.50b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e36.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd 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align=\"left\"\u003e\n\u003cp\u003e1.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00ab\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e74.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.56b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e38.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.51c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e223.26\u0026thinsp;\u0026plusmn;\u0026thinsp;d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e135.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.90c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e23.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.27c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00bc\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.39a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02ab\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e77.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.70a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e42.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e250.75\u0026thinsp;\u0026plusmn;\u0026thinsp;c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e138.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.17b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e24.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.78bc\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.002a\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.30\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03ab\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e77.95\u0026thinsp;\u0026plusmn;\u0026thinsp;1.33a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e43.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10ab\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e257.99\u0026thinsp;\u0026plusmn;\u0026thinsp;b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e141.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.37a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e25.77\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34ab\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.52\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01c\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e79.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.54a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e43.95\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e285.73\u0026thinsp;\u0026plusmn;\u0026thinsp;a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e142.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e26.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.19a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"5\" align=\"left\"\u003e\n\u003cp\u003eRoot stage\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCK\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e19.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.40b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e76.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.22\u0026thinsp;\u0026plusmn;\u0026thinsp;0.45d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e190.31\u0026thinsp;\u0026plusmn;\u0026thinsp;e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e147.99\u0026thinsp;\u0026plusmn;\u0026thinsp;1.05d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e25.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.39d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd 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align=\"left\"\u003e\n\u003cp\u003e28.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.69a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.36\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e79.05\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd 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align=\"left\"\u003e\n\u003cp\u003e140.05\u0026thinsp;\u0026plusmn;\u0026thinsp;0.72e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e27.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34e\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01c\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e20.83\u0026thinsp;\u0026plusmn;\u0026thinsp;0.37b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e88.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e314.13\u0026thinsp;\u0026plusmn;\u0026thinsp;d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e186.78\u0026thinsp;\u0026plusmn;\u0026thinsp;0.23d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e35.08\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01bc\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.43a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e90.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.69ab\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e37.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e358.65\u0026thinsp;\u0026plusmn;\u0026thinsp;c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e185.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e37.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.40c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00ab\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e23.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.20\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e91.36\u0026thinsp;\u0026plusmn;\u0026thinsp;0.26a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e38.19\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e368.88\u0026thinsp;\u0026plusmn;\u0026thinsp;b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e242.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.37a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e53.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e23.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.18\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e89.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.43bc\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e37.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e391.13\u0026thinsp;\u0026plusmn;\u0026thinsp;a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e228.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e46.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.432\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00ab\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd rowspan=\"5\" align=\"left\"\u003e\n\u003cp\u003eHarvesting stage\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCK\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e19.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e82.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.55d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e29.30\u0026thinsp;\u0026plusmn;\u0026thinsp;0.30c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e286.75\u0026thinsp;\u0026plusmn;\u0026thinsp;c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e129.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e17.86\u0026thinsp;\u0026plusmn;\u0026thinsp;0.40d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00d\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e21.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e84.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e30.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.38b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e277.07\u0026thinsp;\u0026plusmn;\u0026thinsp;d\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e144.21\u0026thinsp;\u0026plusmn;\u0026thinsp;0.85c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00ab\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00cd\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e22.77\u0026thinsp;\u0026plusmn;\u0026thinsp;0.59a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.31\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e85.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.60c\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e33.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.25a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e296.16\u0026thinsp;\u0026plusmn;\u0026thinsp;b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e158.82\u0026thinsp;\u0026plusmn;\u0026thinsp;1.02b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e25.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.46\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02ab\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00bc\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e24.26\u0026thinsp;\u0026plusmn;\u0026thinsp;0.91a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e89.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.48a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e34.61\u0026thinsp;\u0026plusmn;\u0026thinsp;0.75a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e295.86\u0026thinsp;\u0026plusmn;\u0026thinsp;b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e170.08\u0026thinsp;\u0026plusmn;\u0026thinsp;0.99a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e29.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.19a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01a\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eT4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e24.16\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.14\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e87.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e31.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e358.10\u0026thinsp;\u0026plusmn;\u0026thinsp;a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e157.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.72b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e25.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.31b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00a\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.43\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03b\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00ab\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eNote: SOM-organic matter; TN-total nitrogen; AN-alkaline nitrogen; AP-rapid phosphorus; AK-rapid potassium; MBC-microbial carbon; MBN-microbial nitrogen; MC-soil water content; SBD-soil bulk density; TP-soil porosity. -MC-soil water content; SBD-soil bulk density; TP-soil porosity. Data are mean\u0026thinsp;\u0026plusmn;\u0026thinsp;standard error. Different letters after the data in the same column indicate significant differences between treatments (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05)\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2 Effect of fermented biogas slurry returning of tail vegetables on soil enzyme activity\u003c/h2\u003e\n\u003cdiv id=\"Sec10\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.1 Effect of fermented biogas slurry returning on urease activity\u003c/h2\u003e\n\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e, the urease activity of the vegetables increased with the application of biogas slurry, and the increase of urease activity also increased with the increase in biogas slurry returned to the field. Specifically, T1, T2, T3 and T4 increased by 5.89%, 3.49%, 4.96%, and 2.41%, respectively, under biogas slurry application. T1, T2, T3 and T4 were significantly higher than CK, but there was no significant difference between T1 and T4, T2 and T3 treatments. At the rosette stage, T1, T2, T3 and T4 increased 4.26%, 5.57%, 5.63% and 5.14%, respectively, with no significant difference between T1 and CK. Treatments T2, T3 and T4 were significantly higher than CK, but there was no significant difference between treatments T2, T3 and T4. Compared to CK, T1, T2, T3, and T4 increased by 8.18%, 9.78%, 12.71%, 1 and 11.02%, respectively, with no significant difference between treatments. T1, T2, T3 and T4 increased by 8.09%, 11.99%, 17.30%, 12.60%, 7.33%, 13.61%, 21.83% and 14.11%, respectively. Urease activity was significantly higher under T1, T2, T3 and T4 treatments than CK, but there was no significant difference between T2 and T4 treatments. Compared with CK, the urease activity increases of T1, T2, T3 and T4 were 4.26%~8.18%、3.49%~13.61%、4.96%~21.83%、5.14%~14.11% respectively.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.2 Effect of fermented biogas slurry returning of tail vegetables on soil sucrase activity\u003c/h2\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n\u003cp\u003eSoil sucrase is a key enzyme that is closely related to soil organic matter and aggregate surface area, and is considered as one of the important measures of soil fertility level and biological activity. Figure\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e shows that with the increase of sucrase activity in the growth period, the sucrase activity of each growth cycle basically showed a positive growth trend with the increase of biogas slurry returned to the field. T1, T2, T3 and T4 increased 10.14%, 10.79%, 11.60%, 11.70% at seedling 1, and the differences between T1, T2, T3 and T4 were not significant, but all were significantly higher than those of CK. Rosette stage T1, T2, T3, T4 increased 12.21%, 16.20%, 17.20%, 22.29%, T1, T2, T3, T4 significantly higher than CK. The growth of T1,71%, T2%, T3, T4,21.19%, T1,11.93%, 11.63%, 18.15%, 19.90% and 9.22%, T1, T2, T3 and T4 were significantly higher than CK, but there was no significant difference between T 1 and T4, T2 and T3 treatments. T1, T2, T3, T4 increased 10.60%, 13.79%, 17.38%, 8.78%, T1, T2, T3, T4 were significantly higher than CK, and there was no significant difference between T1 and T4 treatments. Compared with CK treatment, the increases of T1, T2, T3 and T4 were 8.71%~12.21%, 13.79%~20.19%, 11.60%~21.97%, 8.78%~22.29%.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.3 Effect of fermented biogas slurry returning of tail vegetables on alkaline phosphatase activity\u003c/h2\u003e\n\u003cp\u003eIt can be seen from Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e that that the alkaline phosphatase activity of tail cabbage increased under the fermented biogas slurry treatment in all growth cycles except the harvest period, and that the range of increase increased with the increase in biogas slurry return except at T4. Under biogas slurry treatments, T1, T2, T3 and T4 increased by 4.23%, 5.37%, 5.72% and 4.76% at seedling stage respectively. There were no significant differences between the T1, T2, T3 and T4 treatments, but they were significantly higher than the CK. T1, T2, T3 and T4 increased by 2.85%, 5.77%, 8.16%, 3.57% and 1.95%, 5.38%, 7.96% and 2.56%, respectively, whereas T1, T2, T3 and T4 were significantly higher than those of CK and there was no significant difference between treatments T1 and T4. T1, T2, T3 and T4 increased by 2.36%, 5.89%, 6.60% and 4.40% in the middle stage of balling, and T1, T2, T3 and T4 were significantly higher than those of CK, and there was no significant difference between treatments T2 and T3. T1, T2, T3 and T4 increased by 8.72%, 9.87%, 10.38% and 5.88% at harvest, and T1, T2, T3 and T4 were significantly higher than those of CK, and there was no significant difference between treatments T1 and T2. Compared with CK, the increases in T1, T2, T3 and T4 were 1.95%~8.72%, 5.37%~9.87%, 5.72%~10.38% and 2.56%~5.88%, respectively.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.4 Effect of fermented biogas slurry returning of tail vegetables on catalase activity\u003c/h2\u003e\n\u003cp\u003eCatalase prevents the accumulation of peroxides in the soil by breaking them down in the soil and preventing them from accumulating in living organisms, thereby avoiding damage to crops. It can be seen from Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e that the total catalase activity did not change significantly as the growth period of baby cabbage progressed, but the soil catalase activity showed a decreasing trend with the increase of biogas slurry application to the field in each growth cycle. At the seedling stage, T1, T2, T3 and T4 catalase activity decreased by 1.68%, 3.91%, 4.29% and 6.25% respectively, with no significant difference between T1 and CK, and T2, T3 and T4 were significantly lower than CK. T1, T2, T3 and T4 decreased by 2.28%, 3.92%, 5.75% and 7.94% at rosette stage, T1, T2, T3 and T4 were significantly lower than those in CK, and there were no significant differences between T1 and T2, T3 and T4 treatments. T1, T2, T3 and T4 decreased by 2.72%, 4.44%, 5.25% and 7.43%, respectively, in the early stage of ball formation, while T1, T2, T3 and T4 were significantly lower than those of CK, with no significant difference between treatments T2 and T3. T1, T2, T3 and T4 decreased by 2.24%, 4.22%, 5.47% and 7.80%, respectively in the middle stage of balling, and T1, T2, T3 and T4 were significantly lower than CK, and there was no significant difference between treatments T1, T2 and T3. T1, T2, T3 and T4 decreased by 2.4%, 2.96%, 4.25% and 6.28% at harvest. T1, T2, T3 and T4 were significantly lower than CK, and there was no significant difference between T1, T2 and T3 treatments. During the whole growth period of baby cabbage, the catalase activity of T1, T2, T3 and T4 decreased by 1.68%~2.72%, 2.96%~4.44%, 4.25%~5.75% and 6.25%~7.94% compared to CK treatment.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n\u003ch2\u003e2.3 Correlation analysis of soil physicochemical factors and enzyme activity\u003c/h2\u003e\n\u003cp\u003eThe correlation analysis between soil enzyme activity and physicochemical properties of soil (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e) indicate that there was a significantly positive correlation between soil urease activity and alkaline nitrogen, soil water content, MBC, MBN and quick acting phosphorus (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05); soil sucrase activity and soil organic matter, alkaline nitrogen, quick phosphorus, MBC, MBN, total nitrogen, soil moisture content and soil bulk density showed a significant positive correlation (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05); There was a significant positive relationship between alkaline phosphatase activity and alkaline hydrolysis nitrogen, MBC, MBN, organic matter, total nitrogen content and water content (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05); A significant positive correlation was found between catalase activity and soil rapid phosphorus and total nitrogen content (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n\u003ch2\u003e2.4 Comprehensive evaluation of soil fertility under different fertilization treatments\u003c/h2\u003e\n\u003cp\u003eThe correlation of fertilization treatment with soil physicochemical properties and enzyme activity not only reflects the relationship between soil substances and nutrients in the energy cycle and transformation process, but also emphasizes the important role of soil enzymes as microbial activity indicators in the soil biochemical process[\u003cspan class=\"CitationRef\"\u003e19\u003c/span\u003e]. To evaluate the effects of fertilization on soil fertility (including physicochemical properties and enzyme activities), a principal component-cluster analysis was performed for ten variables including soil organic matter, total nitrogen, alkali hydrolyzable nitrogen, available phosphorus, total nitrogen, MBC, MBN, urease, sucrase, and phosphatase activities at the harvest period (KMO: 0.761, P\u0026thinsp;\u0026lt;\u0026thinsp;0.005) according to the research protocol of Chen et al [\u003cspan class=\"CitationRef\"\u003e20\u003c/span\u003e]. As shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e, one principal component with an eigenvalue greater than 1 was extracted, reflecting 82.28% of the original information (i.e., the cumulative contribution rate of variance was 82.28%), and no original variable was lost. Therefore, it is reliable to use 7 physicochemical indexes and 3 soil enzyme activity indexes selected in this paper to evaluate different fertilization treatments.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u0026nbsp;\u003c/div\u003e\n\u003cdiv class=\"colspec\" align=\"char\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003ctable id=\"Tab4\" border=\"1\"\u003e\u003ccaption\u003e\n\u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n\u003cdiv class=\"CaptionContent\"\u003e\n\u003cp\u003eEigenvalues, variance contributions and factor component shares of principal component analysis\u003c/p\u003e\n\u003c/div\u003e\n\u003c/caption\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003cth rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003eingredient\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"3\" align=\"left\"\u003e\n\u003cp\u003eInitial eigenvalue\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"3\" align=\"left\"\u003e\n\u003cp\u003eInitial factor loadings sum of squares\u003c/p\u003e\n\u003c/th\u003e\n\u003cth colspan=\"2\" align=\"left\"\u003e\n\u003cp\u003ePrincipal Component Matrix\u003c/p\u003e\n\u003c/th\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eeigenvalue\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003evariance contribution(%)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCumulative contribution (%)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eeigenvalue\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eVariance contribution (%)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCumulative contribution (%)\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003efactor\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd rowspan=\"2\" align=\"left\"\u003e\n\u003cp\u003epercentage\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003ePercentage of variance\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCumulative %\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003etotal\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003ePercentage of variance\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eCumulative %\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e8.229\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e82.289\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e82.289\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8.2289\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e82.289\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e82.289\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eMBN\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.991\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.885\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8.847\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e91.137\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eMBC\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.990\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e3\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.261\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.611\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e93.738\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eURE\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.986\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e4\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.210\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e2.101\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e95.849\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAN\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.921\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e5\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.197\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.969\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e97.818\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eINV\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.907\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e6\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.129\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e1.290\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e99.108\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eSOM\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.877\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e7\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.047\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.470\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e99.578\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAP\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.877\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e8\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.024\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.244\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e99.822\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eAK\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.869\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e9\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.016\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.155\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e99.977\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eALP\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.818\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e10\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.002\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e0.023\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003e100.000\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n\u003ctd align=\"left\"\u003e\n\u003cp\u003eTN\u003c/p\u003e\n\u003c/td\u003e\n\u003ctd align=\"char\" char=\".\"\u003e\n\u003cp\u003e0.813\u003c/p\u003e\n\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003ctfoot\u003e\n\u003ctr\u003e\n\u003ctd colspan=\"9\"\u003eNote: MBN - microbial nitrogen; MBC - microbial carbon; URE - urease activity; AN - alkaline nitrogen removal; INV - sucrase activity; SOM - organic matter; AP -quick-acting phosphorus; AK-quick-acting potassium; ALP-alkaline phosphatase activity; TN-total nitrogen;\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tfoot\u003e\n\u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe extracted principal component weights were calculated based on the raw data and feature values, combined with the data after standardization (eliminating data magnitude and their contribution rate), the successful component score function expression: F\u0026thinsp;=\u0026thinsp;0.1204 MBN\u0026thinsp;+\u0026thinsp;0.1203 MBC\u0026thinsp;+\u0026thinsp;0.1198 urease activity\u0026thinsp;+\u0026thinsp;0.1119 alkaline nitrogen\u0026thinsp;+\u0026thinsp;0.10.1102 sucrase activity\u0026thinsp;+\u0026thinsp;0.1066 organic matter\u0026thinsp;+\u0026thinsp;0.1066 rapid phosphorus\u0026thinsp;+\u0026thinsp;0.1056 rapid potassium\u0026thinsp;+\u0026thinsp;0.0994 phosphatase activity\u0026thinsp;+\u0026thinsp;0.0988 total nitrogen. The sum of the main component of the composite score and its contribution rate, there is only one principal component in this study, so the comprehensive score Z\u0026thinsp;=\u0026thinsp;FI 82.289%. The comprehensive score was classified as a new index for clustering, and the soil fertility was sorted as T3\u0026thinsp;\u0026gt;\u0026thinsp;T2\u0026thinsp;\u0026gt;\u0026thinsp;T4\u0026thinsp;\u0026gt;\u0026thinsp;T\u0026thinsp;\u0026gt;\u0026thinsp;T1\u0026thinsp;\u0026gt;\u0026thinsp;CK (as shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e)\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Effects of fertilization on soil physicochemical factors\u003c/h2\u003e \u003cp\u003eBasic physicochemical factors such as nitrogen, phosphorus, potassium, MBC, MBN and the moisture content of the soil in soil directly reflect the ability of the soil to provide the nutrients needed for crops. Long-term use of chemical fertilizers, coupled with the absorption and elimination of alkali cations by plants, can easily lead to soil acidification, compaction and fixation or loss of nutrients [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Studies have shown that the application of biogas slurry have a tendency to increase the content of soil organic matter, total nitrogen, available phosphorus and other nutrients compared to chemical fertilizers alone, but the excessive application of biogas slurry did not further increase soil nutrients [\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. In this study, compared with CK, the contents of soil organic matter, total nitrogen, alkaline hydrolyzable nitrogen, available phosphorus and microbial biomass carbon (nitrogen) were increased by 2.45%~22.97%, 1.29%~24.49%, 1.10%~17.02%, 2.51%~22.23%, 5.6%~76.56% and 9.49%-104.9%, respectively, because the biogas slurry introduced some nutrients [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] or some beneficial microorganisms, such as phosphate-solubilizing bacteria, which increases the effectiveness of phosphorus [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAs the growth cycle of baby vegetables advances, the organic matter content in the soil under the fermented biogas slurry of tail vegetables returned to the field showed an increasing trend, which is due to the organic matter brought in by the digestate [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], but with the increase in the amount of tfermented biogas slurry of tail vegetables returned to the field and the passage of time and the effect of the growth of organic matter will be gradually weakened. On the one hand, as the amount of the fermented biogas slurry of tail vegetables returned to the field increased, the possible decomposed substances in the soil increased, and the soil was in a saturated state, so the effect of organic matter growth was weakened by continuing to increase the amount of biogas slurry returned to the field. On the other hand, with the passage of time, the organic matter that is easily decomposed in the soil is gradually degraded, and the remaining organic material is more difficult to decompose, which leads to the slowdown of the decomposition rate of organic matter and limits the growth of organic matter.Soil total nitrogen \"S\" trend, it is closely related to crop growth characteristics and fertilization strategy, seedling, rosette, baby vegetables small and limited absorption of nitrogen in soil nitrogen accumulation, early, middle, baby vegetable growth of massive consumption of nitrogen in the soil, and harvesting period baby vegetables mainly internal material conversion, reduce the absorption of nitrogen, so the nitrogen in the soil and began to accumulate [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. The content of alkaline hydrolyzable nitrogen in the soil first increased and then decreased, which may be related to the fertilization method and the fertilization period. Since there was no fertilization was applied after nitrogen supplementation at the middle stage of balling, the alkaline hydrolyzable nitrogen content decreased at the harvest stage under the loss of crop absorption consumption, nitrogen leaching and volatilization. At each growth stage, the alkaline-hydrolyzable nitrogen content was higher than that of the CK under each fertilization treatment, which may be related to the morphology of the nitrogen brought into the biogas slurry and the ability of the biogas slurry to increase urease activity [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], which is consistent with the trend that the alkaline-hydrolyzable nitrogen content first increased and then decreased during the growth period of potato by chemical fertilizer combined with organic fertilizer according to Du et al [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. The quick-acting phosphorus in the soil showed a decreasing trend with the advancement of the fertility stage of baby cabbage, which may be because the phosphorus fertilizer was applied as the base fertilizer at one time, and the available phosphorus was continuously consumed during the growth period. At each growth stage, the content of available phosphorus in soil under application of biogas slurry was higher than CK, which may be related to the form of phosphorus introduced by biogas slurry (mainly available phosphorus), which was proved by NIYUNGEKOC et al [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Both MBC and MBN in the soil first increased and then decreased. This may be related to fertilization and the external ambient temperature. The Seedling and rosette stage, initial fertilization and temperature increase the number of soil microorganisms, causing the MBC and MBN to increase. High external temperature in the middle knot stage and harvest period, decreased number of soil microorganisms, so both showed a downward trend. With the increasing return of biogas slurry during each growth stage, MBC and MBN were higher than CK with only chemical fertilizer, This may be because the tail vegetables fermented biogas slurry brings in a large number of microorganisms, This is consistent with the conclusion by Chai et al [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] who revealed that replacing chemical fertilizer studied with biogas slurry in asparagus field can significantly improve the carbon and nitrogen content of soil microorganisms.\u003c/p\u003e \u003cp\u003eThe present study showed that soil organic matter, total nitrogen, alkaline dissolved nitrogen, quick-acting phosphorus, MBC and MBN content generally increased and then decreased with the increase in the amount of biogas slurry applied to the field from taille vegetable fermentation, which is consistent with the results of Yan et al [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] who showed that the concentrations of SOM, AN, AP, AK and TN in soil first increased and then decreased with the increase in biogas slurry application. This may be because the excessive application of biogas slurry leads to the accumulation of salt or the introduction of some harmful substances, which suppresses microbial activities, and then affect the decomposition of organic matter and the release of nutrients [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Combined with this test, the T3 treatment had the best effect in promoting soil fertility. Compared with CK in the same period, organic matter, total nitrogen, alkaline nitrogen, quick phosphorus, and microbial carbon (nitrogen) increased by 13.68%~22.79%, 6.29%~21.83%, 5.81%~17.02%, 144.74% ~ 18.11%, 10.27%~75.56%, 21.26%~104.91%, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Effect of fertilization treatments on soil enzyme activities\u003c/h2\u003e \u003cp\u003eSoil physical and chemical indicators have always played an important role in the assessment of soil quality and fertility, but under the influence of changing environmental conditions and anthropogenic activities, these traditional indicators are no longer able to comprehensively reflect the quality of soil, so that in recent years the enzyme activity of soil has been emphasized as a comprehensive indicator by scientists [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. Urease converts nitrogen into ammonia or ammonium nitrogen which can be directly absorbed and utilized by the crop by catalyzing the hydrolysis of urea. Therefore, urease activity is used as an important indicator of the status soil nitrogen supply [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Our results found that the return of biogas slurry can improve urease activity, which may be due to the fact that the fermentation of biogas slurry stimulates the activity of microorganisms and improves the metabolism of soil microorganisms, thus improving enzyme activity [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. During the growth period of baby cabbage, the dynamic changes of soil urease are closely correlated with the growth stage of plants. In particular, soil urease and alkaline phosphatase showed the lowest activity at the seedling stage, which may be related to the level of fertilizer demand, soil temperature and seasonal factors. Enzyme activity decreases when the hydrothermal conditions in the soil impair the microbial function of the soil, which is consistent with the findings of Emmert et al [\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. From the rapid growth of baby cabbage to the middle of the ball, because baby cabbage needs more nutrients, soil microorganisms need to secrete more biological enzymes to transform.When the crop stops growing during the harvesting period, the activity of the enzyme decreases. Sucrase breaks down sucrose into glucose and fructose, which provide direct nutrients for soil microorganisms and plant roots, and its activity reflects soil organic carbon storage and its decomposition process and is an indicator of the level of soil fertility and the degree of soil maturation [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. In this experiment, it was found that sucrase activity increased from the seedling stage to the early nodulation stage and decreased at the middle stage of nodulation and harvest, which may be due to temperature and the \"slow-fast-slow\" growth characteristic of plant growth. At the seedling and rosette stages of baby cabbage, sucrase activity was low because the root system was small, and the biosolids had just been applied, and soil temperature was low. However, with the growth of baby cabbage, the expansion of the root system, the increase in temperature and the accumulation of biosolids, sucrase activity gradually increased and finally peaked in the early nodulation stage, and then led to the decline of sucrase activity in the soil with the reduction of plant growth and excessively high temperatures [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e]. Sucrase activity increased and then decreased as the amount of biogas slurry increased. Under the replacement of T4 biogas slurry, the sucrase activity was lower than that under the T3 treatment, which is consistent with the results of ZHang et al [\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e]. The reason could be that the high concentration of biogas slurry returned to the field contains some substances that inhibit sucrase activity, or that when there are too many organic substances in the biogas slurry, the microorganisms preferentially utilise other carbon sources and reduce the degradation of sucrose, resulting in a decrease in sucrase activity [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e]. Alkaline phosphatase can reflect the phosphorus supply capacity of the soil by hydrolyzing the organic phosphorus compounds in the soil and providing plants with directly available phosphorus [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. The present experiment showed that the returning fermented biogas slurry from tail vegetables to the field could significantly increase the soil alkaline phosphatase activity, which could be attributed to the rich organic matter in the biogas slurry, which stimulated microbial metabolic activities and led to an increase in alkaline phosphatase activity. This is consistent with the findings of ZHu et al [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. From seedling stage to mid-balling stage of baby cabbage, the alkaline phosphoric acid activity increased as the growth stage of cabbage progressed, which may be due to two reasons; Firstly, the microbial activity and enzyme activity increase with the increases in temperature, and secondly, the pH of biogas slurry itself is high, and the continuous accumulation of biogas slurry in the seedling stage, rosette stage, early stage of balling and middle stage of balling leads to the increase of pH value around the rhizosphere and promotes the increase of alkaline phosphatase activity, while the decrease of alkaline phosphatase activity at harvest stage may be due to the high soil temperature and the decrease of enzyme activity. Previous studies have shown that a large amount of biogas slurry returned to the field increases pH, decreases acidic phosphoric acid activity, and increases alkaline phosphatase activity [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e].Catalase is commonly found in soil microorganisms and mainly decomposes hydrogen peroxide which is harmful to organisms, protects soil microorganisms and plant roots from oxidative damage, and characterizes the activity of soil oxidation processes and the intensity of soil biochemistry [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. In this study, it was found that as the growth period of baby cabbage progressed, there was no significant change in hydrogen peroxide activity under each fertilization treatment, which may be related to the short application cycle of biogas slurry[\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e], and in this experiment, which may be related to the abundant active substances in the biogas slurry, which can degrade toxic substances such as peroxide in the rhizosphere and protect the root system to maintain normal physiological function, which was confirmed by the results of Guan et al [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e]. Zhang et al [\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e] found that the return of straw significantly increased soil sucrase and urease activities in soil, but had no significant effect on catalase activity.\u003c/p\u003e \u003cp\u003eIn conclusion, this study showed that the return of fermented biogas slurry from tail vegetables increased the activities of urease, sucrase and alkaline phosphatase in soil, which may be due to the stimulation of the activity of microorganisms and the improvement of the metabolism of soil microorganisms, thereby improving enzyme activity[\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e]. This is in line with previous studies showing that biogas slurry has a positive correlation with the activities of sucrase and alkaline phosphatase [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. In this study, the activities of urease, sucrase and alkaline phosphatase were lower under T4 (biogas slurry) treatment than under T3, suggesting that the biogas slurry should be returned to the field in moderation. This could be due to salt accumulation stress caused by excessive biogas slurry application, which limited root system development, inhibited the number and activity of soil microorganisms, and directly affected enzyme activity [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. Studies have shown that the appropriate application of nitrogen, phosphorus and potassium fertilizers under the biogas slurry rate or by reasonably controlling the carbon to nitrogen ratio in the soil can significantly improve the activity of soil enzymes [\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e], so returning biogas slurry to the field is an important way to improve soil fertility from the perspective of soil enzymes. It has also been shown that the combination of nitrogen, phosphorus and potassium fertilizers at appropriate biogas slurry levels or by reasonably regulating the carbon and nitrogen ratio in the soil can significantly improve the activity of soil enzymes [\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e], and from the perspective of soil enzymes, returning methane gas from taille fermentation to the field is an important way to improve soil fertility.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Effect of correlation between soil physicochemical factors and enzyme activities under fertilization treatments\u003c/h2\u003e \u003cp\u003eThe availability of nutrients in the soil is strongly correlated with the activity of soil enzymes, which could be due to a positive feedback between the two [\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e]. Significant positive correlations between soil urease activity and alkali dissolved nitrogen, soil water content, MBC, MBN and fast-acting phosphorus indicate the importance of urease activity in indicating soil N availability and soil microbial vigor. Yuan et al [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. found a positive correlation between soil nutrients and microbial communities because microorganisms supply soil with C and N and thus improve soil fertility, and the reason analyzed may be that urease is produced by microorganisms and is involved in the degradation of urea. MBC and MBN are indicators of microbial abundance and activity in the soil, microorganisms obtain and release nutrients such as carbon and nitrogen through the decomposition of organic matter and substrates such as urea, which can provide more substrates for the urease reaction, thus increasing urease activity. In addition, appropriate soil moisture content can create suitable environmental conditions for microbial growth and metabolism, which can increase urease activity. Sucrase activity in soil was significantly and positively correlated with soil organic matter, alkaline dissolved nitrogen, quick-acting phosphorus, MBC, MBN, total nitrogen, soil water content and soil bulk density, indicating that sucrase activity is closely related to the nutrient status and structure. Organic matter is the main substrate for sucrase, and increasing its content can promote higher sucrase activity. Higher levels of alkaline dissolved nitrogen and fast-acting phosphorus may have provided microorganisms and sucrase with more nutrients and thus promoted sucrase activity; sucrase is produced by microbial metabolism and is involved in the degradation of sucrose; microorganisms obtain carbon and nitrogen sources by decomposing organic matter and substrates; higher MBC, MBN and total nitrogen in the soil are available to microorganisms and sucrase, which promotes sucrase activity; suitable soil conditions such as soil temperature, water content and lower soil bulk density favor the activities of microorganisms and enzymes [\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e]. Soil alkaline phosphatase activity showed significant positive correlations with alkaline dissolved nitrogen, MBC, MBN, organic matter, total nitrogen and water content, suggesting that alkaline phosphatase effectively controls the degree of soil fertility and the moisture status of the soil. Alkaline phosphatase is produced by microbial metabolism and is an enzyme involved in the mineralization process of organophosphate. MBC and MBN characterize microbial abundance, higher levels of organic matter, total nitrogen and alkaline dissolved nitrogen can provide more substrate for alkaline phosphatase, which promotes enzyme activity; higher soil water content can provide suitable environmental conditions to promote microbial growth and metabolism, which in turn increases enzyme activity [\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e]. Catalase activity showed a significant positive correlation with fast phosphorus and total nitrogen content in soil. Catalase plays an important role in redox reactions. The content of fast-acting phosphorus and total nitrogen may affect the redox environment of the soil, and a suitable redox environment has an important influence on catalase activity. Higher levels of fast-acting phosphorus and total nitrogen may help to maintain a suitable redox environment, which promotes catalase activity.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Effect of fertilization treatments on overall soil fertility\u003c/h2\u003e \u003cp\u003eThe physical and chemical properties of the soil can affect the enzyme activity in the soil, while the enzyme activity reflects the biological activity and the ability to provide substances and nutrients in the soil. Soil enzyme activity and soil physical and chemical properties were calculated by downscaling and weighting to obtain a composite score, and fertilizer treatments were evaluated accordingly. In this study, as the amount of biogas slurry returned to the field increase, the comprehensive score of each treatment first increased and then decreased, indicating that the return of biogas slurry had a positive effect on soil fertility, which is consistent with the results of Wang et al [\u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e]. The score of T3 treatment was the highest in fertilization treatment, and the score decreased in the T4 treatment, indicating that an appropriate amount of biogas slurry should be returned to the field. An inappropriate amount of biogas slurry returned to the field will lead to an imbalance of various physical and chemical indices and enzyme activities, and excessive or low application of biogas slurry would lead to the imbalance of soil nutrients, microbial activities and enzyme activities, resulting in poor soil comprehensive fertility. Chai et al [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e] showed that the substitution of chemical fertilizer with biogas slurry by 50% could significantly increase the content of soil organic matter and available potassium, but have no significant effect on total nitrogen, alkali hydrolyzable nitrogen and available phosphorus, and the substitution of chemical fertilizer with biogas slurry by 100% increased sucrase activity and urease activity, but decreased phosphatase. ZHao et al [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] showed that the application fermented biogas slurry of taille vegetables could significantly maintain the production yield of cauliflower and improve the quality of cauliflower, but the excessive application could greatly reduce the utilization rate of nitrogen.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003e(1)The return fermented biogas slurry of taille vegetables to the field significantly increased the content of soil organic matter, total nitrogen, alkaline dissolved nitrogen, quick-acting phosphorus, quick-acting potassium, microbial carbon and microbial nitrogen, and the soil porosity tended to increase, the soil bulk density tended to decrease and had a relatively small effect on soil moisture content. The increase of organic matter, total nitrogen, alkaline-hydrolyzable nitrogen, available phosphorus, available potassium, microbial biomass carbon and microbial biomass nitrogen under T3 (246m\u003csup\u003e3\u003c/sup\u003e\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e taille vegetables fermented biogas slurry\u0026thinsp;+\u0026thinsp;44kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e chemical nitrogen) was 13.66\u0026thinsp;~\u0026thinsp;21.48%, 6.29\u0026thinsp;~\u0026thinsp;21.83%, 5.81\u0026thinsp;~\u0026thinsp;17.03%, 4.74\u0026thinsp;~\u0026thinsp;18.11%, 3.18\u0026thinsp;~\u0026thinsp;47.89%, 10.27\u0026thinsp;~\u0026thinsp;76.58% and 21.27\u0026thinsp;~\u0026thinsp;104.94%, respectively.\u003c/p\u003e \u003cp\u003e(2)The return of fermented biogas slurry of tail vegetables to the field significantly increased the activities of the soil enzymes urease, sucrase and alkaline phosphatase, but had little effect on catalase activity, and there was no significant difference. After biogas slurry application, the activities of soil enzymes such as urease, sucrase and alkaline phosphatase increased by 2.41\u0026ndash;21.83%, 8.71%~22.29% and 1.95%~10.38%, respectively, among which T3 treatment increased by 0.96\u0026ndash;21.83%, 11.7%~21.97% and 5.72%~10.38%.\u003c/p\u003e \u003cp\u003e(3)The cluster analysis was carried out with the composite score value of the principal components as the new index, and the soil fertility under fertilization treatments was in the order of T3\u0026gt;T2\u0026gt;T4\u0026gt;T1\u0026gt;CK, and the T3 treatment had the highest composite score and the best fertility.\u003c/p\u003e \u003cp\u003eConsidering the comprehensive effects of fermented biogas slurry of tail vegetables fertilization treatments on soil physicochemical properties, soil microbial function and baby cabbage production performance, the ratio of 75% biogas slurry nitrogen and 25% chemical nitrogen in fertilization treatment had the best effect.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAuthor Contributions: Conceptualization, S.Z.Y. and R.C.; methodology, B.L. and S.Z.Y.; software, J.H.; validation, S.Z.Y. and B.L.; resources, S.Z.Y and R.C.; data curation, J.H.; writing\u0026mdash;original draft preparation, S.Z.Y.; writing\u0026mdash;review and editing, R.C., and S.Z.Y.; supervision, R.C.; project administration, S.Z.Y.; funding acquisition, R.C.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData availability statementsThe datasets generated and/or analysed during the current study are not publicly available due [Considering that the article is not yet published, there is a possibility of plagiarism/plagiarism, so I don't want to provide all the raw data, if the editorial department feels that some of the data needs raw data because of the review needs, they can contact themselves at any time, and they will provide the corresponding data. If the article is published at a later stage, I can provide the corresponding data] , but are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHe, R.; Shao, C.; Shi, R.; Zhang, Z.; Zhao, R. Development Trend and Driving Factors of Agricultural Chemical Fertilizer Efficiency in China. \u003cem\u003eSustainability\u003c/em\u003e 2020, \u003cem\u003e12\u003c/em\u003e.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAbe, S.S.; Hashi, I.; Masunaga, T.; Yamamoto, S.; Honna, T.; Wakatsuki, T. Soil Profile Alteration in a Brown Forest Soil under High-Input Tea Cultivation. Plant. Prod. Sci. 2006, \u003cem\u003e9\u003c/em\u003e, 457\u0026ndash;461.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang; Tian'An; Chen; Han; Y.; H.; Ruan; Honghua. Global negative effects of nitrogen deposition on soil microbes. 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Energy Issue 2008, \u003cem\u003e29\u003c/em\u003e, 284\u0026ndash;293.\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":"fermented biogas slurry of tail vegetables, enzyme activity, soil fertility,","lastPublishedDoi":"10.21203/rs.3.rs-4333390/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4333390/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eObjective\u003c/strong\u003e The objective of this study is to study the effects of fermented biogas slurry derived from tail vegetables on soil physicochemical properties and enzyme activities, and to evaluate soil fertility.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethod \u003c/strong\u003eBaby cabbage cultivated in the field, five treatments with iso-nitrogen fertilization were set up: CK (no biogas liquid nitrogen), T1 (25% biogas liquid nitrogen), T2 (50% biogas liquid nitrogen), T3 (75% biogas liquid nitrogen) and T4 (100% biogas liquid nitrogen).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults \u003c/strong\u003eIt was found that returning biogas slurry from the fermentation of tail vegetables to the field significantly increased soil organic matter, total nitrogen, alkaline dissolved nitrogen, available phosphorus, available potassium, and microbial carbon (nitrogen) content, improved soil porosity and decreased soil bulk density, with little effect on soil water content; Fermentation of biogas slurry from tail cabbage significantly increased the activities of urease, sucrase and alkaline phosphatase, but had little effect on catalase activity, and the increases of urease, sucrase and phosphatase activities were 3.49%~21.83%, 8.71%~22.29% and 1.95%~10.38%, respectively. Through principal component cluster analysis, the weighted comprehensive score was used as a new index, and soil fertility was comprehensively evaluated as T3\u0026gt;T2\u0026gt; T4\u0026gt;T1\u0026gt;CK.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion\u003c/strong\u003e Considering the comprehensive effects of fermented biogas slurry fertilization on soil physicochemical properties and soil enzyme activities, the fertilization effect T3 (246m3·hm-2\u0026nbsp;tail vegetable fermentation biogas slurry + 44kg·hm-2\u0026nbsp;pure chemical nitrogen) was the best and the comprehensive fertility was the best.\u003c/p\u003e","manuscriptTitle":"Effects of fermented biogas slurry returning of tail vegetables on soil enzyme activity and fertility","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-09 05:28:51","doi":"10.21203/rs.3.rs-4333390/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":"eec6897d-f948-4038-81d2-164193063238","owner":[],"postedDate":"May 9th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":31600537,"name":"Biological sciences/Ecology"},{"id":31600538,"name":"Biological sciences/Plant sciences"}],"tags":[],"updatedAt":"2024-09-30T03:53:34+00:00","versionOfRecord":[],"versionCreatedAt":"2024-05-09 05:28:51","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4333390","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4333390","identity":"rs-4333390","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}