Optimizing planting density and nitrogen input for improved nitrogen use efficiency, yield and seed quality in sesame

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Although dense planting has been adopted by some sesame farmers to improve yield, the practice lacks optimization. Hence, this study was conducted to determine an optimal planting density (PD) and nitrogen (N) application rate for enhancing sustainable sesame production and quality. We simultaneously investigated the impacts of PD and N-dose on sesame nitrogen use efficiency (NUE), biomass production, N allocation to organs, and seed yield and quality. Through field experiments under different PDs and N supplies and statistical analyses, we identified 190,000 plants·hm − 2 (PD) and 60 kg·hm − 2 (N-dose) as optimal conditions for sustainable improvement of sesame production. Notably, sesame yield, NUE, biomass accumulation, and seed quality traits, including protein content, fat content, and fatty acid composition, were maximal under these optimal conditions. The nitrogen allocated to seeds under these optimal conditions was significantly higher than that to stems, leaves, and capsules. Correlation analysis revealed that PD is significantly negatively associated with the number of capsules, seed number per capsule, 1000-seed weight, protein content, and linoleic acid content. N rate exhibited a significant positive correlation with protein content, total biomass, and total N content, as well as a significant negative correlation with NUE. Our findings may guide land-use efficiency for sesame farming systems and contribute to the sustainable production of high-quality sesame. Earth and environmental sciences/Environmental sciences Biological sciences/Plant sciences planting density nitrogen application sesame yield NUE Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction Higher crop yield per unit area (YPUA) is crucial to guarantee food security. Among the factors that influence crops’ YPUA include principally PD and N supply (Wu et al., 2023 ; Zhao et al., 2023 ). Sparse planting and a higher N dose can facilitate N availability for plants (Stockmann et al., 2019 ). However, it is vital to gain a higher yield through the group effect (Hou et al., 2019 ; Huang, Chen, Cao, & Zou, 2018 ; Zhi et al., 2016 ). Accordingly, studies revealed that increasing PD combined with an appropriate N dose significantly improves crop yield (Duan, Wei, Soualiou, & Zhou, 2023 ). Dense planting coupled with reduced N dose is one of the key strategies in green agricultural production (Basso, Cammarano, Troccoli, Chen, & Ritchie, 2010 ). Unfortunately, PD and N doses have not yet been optimized for major nutritional crops, limiting efforts to mitigate environmental risks associated with intensive agricultural practices. Sesame is an important cash crop for smallholder farmers in growing countries (Dossa, Konteye, Niang, Doumbia, & Cissé, 2017 ). Of the different sesame types, black sesame presents the most health benefits, nutritional values, and food industrial applications (Xu et al., 2024 ). In upland hilly red soil regions of southern China, black sesame is of higher economic value for smallholders. Unfortunately, in the past 10 years, the YPUA of black sesame has been increasing slowly, while the available arable land is decreasing significantly. Farmers often apply more N fertilizer to improve seed yield (Kalaiselvan P., 2024 ). For instance, in China, some farmers plant sesame at extremely wide spacing, and they think that the low density with high N nutrition can make sesame plants strong and produce more capsules. Yet, limited research was conducted to support this ecotoxic statement. High N application rates often lead to nitrogen loss, causing environmental pollution and food security concerns (Wang, 2017 ). Researchers have recently found that yield is closely related to capsule numbers in sesame, and capsule numbers per unit area increased significantly with PD (Ramazani, 2016 ). Increased density causes competition for nutrition, water, and light among plants. However, the dry matter and leaf area index of sesame increased significantly under dense planting conditions. Thus, PD and N input rates are critical factors influencing sesame yields (Rui-qing et al., 2017; Zenawi & Mizan, 2019a , 2019b ). However, still less is known regarding the combined effects of these two factors on yields and seed quality in sesame. Studies have shown that high N rates increase the protein content of crop grains but reduce the levels of secondary metabolites and certain nutrients (Khan et al., 2018 ; Mostashari & Mousavi Khaneghah, 2024 ; Baoqiang Zheng et al., 2020 ). Sesame is a nutrient-rich and functional food highly appreciated for its quality value (Deme, Narasimhulu, & Parthasarathy, 2018 ). Its seeds comprise 45 ~ 65% oil, 19 ~ 35% protein, and 14 ~ 20% carbohydrates (Mostashari & Mousavi Khaneghah, 2024 ; Xu et al., 2024 ). Sesame seed oils are rich sources of unsaturated fatty acids (UFA) (mainly 35.9 ~ 42.3% oleic acid and 41.5 ~ 47.9% linoleic acid). The saturated fatty acids (SFA) (palmitic acid 7.9 ~ 12% and stearic acid 4.8 ~ 6.1%) represent less than 20% (Mostashari & Mousavi Khaneghah, 2024 ; Xu et al., 2024 ). Cultivating nutrient-rich and high-yielding sesame varieties is one of the major breeding goals. Hence, it is vital to determine an optimal PD and N application rate to improve the sustainable production of high-quality sesame seeds. Sustainable measures are the best approaches to enhance crop-derived products’ quality and quantity for human consumption (Nosheen et al., 2019 ). In the present study, we investigated the combined effects of PD and N application rates on sesame NUE, yield, and quality components in the field under a hilly red soil region in southern China. We aimed to determine an optimal PD and N rate for increasing sesame NUE, YPUA, and quality. 2. Methods and Materials 2.1. Experimental design Field experiments were conducted in 2022 at the Jiangxi Agriculture University (28.45°N, 1115.49°E, 78 m altitude), Jiangxi Province, China. The site is located in a subtropical monsoon climate zone and a hilly red soil region in southern China. The soil characteristics were as follow: pH = 4.73, organic matter = 15.51 g·kg − 1 , total N = 0.13%, available nitrogen N = 102.66 mg·kg − 1 , available P = 31.49 mg·kg − 1 , available K = 148.48 mg·kg − 1 . Average daily temperatures (minimum and maximum) and rainfall during the experiment period are shown in Figure S1 . A black sesame cultivar, ‘Jinhuangma’ was used in this experiment. It has been adopted by farmers due to its high yield and palatability. The trial was designed using a randomized block design with four replications, considering two factors: different N application rates and different PDs. N fertilizer was applied as urea at 0, 30, 40, 60, 80, 90, and 120 kg·hm − 2 (labeled N0, N30, N40, N60, N80, N90, and N120, respectively). PDs were 110,000, 150,000, 190,000, 250,000, and 410,000 plants·hm − 2 (termed D11, D15, N19, D25, and D41, respectively). The plot size was 16 m 2 (4 m × 4 m). The plots were distanced by 0.5 m to prevent cross-contamination and treatment effects. When 2–3 pairs of leaves grew, the seedlings were thinned according to the corresponding density. Phosphate (P₂O₅) and potassium (K₂O) fertilizers were applied (sprinkled before sowing) once as a basal at the rate of 50 kg·hm − 2 and 100 kg·hm − 2 , respectively. 2.2. Grain yield, yield components, and biomass Three evenly grown plants were chosen from each plot and harvested when they were fully mature. The 1000-grain weight, the seed number per capsule, and the number of capsules per plant were counted. Stems, leaves, flowers, shells, and seeds were dried at 105°C for 30 min, followed by 70°C for 72 h, and then weighed. The total dry matter accumulated = the sum of the dry weights of each component. 2.3. Nitrogen uptake The dry matter was ground into powder and used to determine N content in each tissue using the Kjeldahl method. Nitrogen accumulation in each tissue was calculated as N content multiplied by the dry matter accumulation. Total nitrogen accumulation of the whole plant is the sum of the N accumulated in each tissue. Nitrogen use efficiency (NUE, %) = (N accumulation in plants at maturity under N application - N accumulation in plants at maturity under control) / N rates×100 N uptake efficiency (NUpE, kg·kg − 1 ) = Total N accumulated in plants / N rates N utilization efficiency (NUtE, kg·kg − 1 ) = Yield/ Total N accumulated in plants Agronomic efficiency of N fertilizer (AEN, %) = (Yield under N application - Yield under control) / N rates 2.4. Oil content, fatty acid composition, and protein content Oils, fatty acid composition, and protein content were determined using near-infrared spectroscopy (严圭 et al., 2020). The seeds were harvested at maturity, and samples were detected by a DS2500F-type near-infrared spectrometer (Foss, USA) and repeated three times. 2.5. Data analysis All statistical analyses were performed using IBM SPSS Statistics 24 (SPSS Inc., USA). Mean differences were determined using the Duncan test at P < 0.05. Figures were generated using Origin 2021 software. 3. Results 3.1. Optimal plant density and nitrogen dose for higher sesame seed yield per unit area To identify an optimal N rate and PD for maximizing sesame YPUA, the black sesame cultivar ‘Jinhuangma’ was cultivated under different N doses and PDs. We found that both nitrogen rates and PD significantly affected seed yield and yield components ( Fig. 1 A-E ) . Under the same PD, the yield, seed weight per plant, capsule number per plant, seed number per capsule, and thousand-seed weight increased significantly with the N dose, then stabilized from an N rate of 60 kg·hm − 2 (Fig. 1 A-E). The best yield performances were obtained at the PD of 190,000 plants·hm − 2 , with the highest yield recorded for an N dose of 60 kg·hm − 2 (D19N60) (Fig. 1 A). Under the same N dose, seed weight and number of capsules per plant decreased significantly with the increase in PD (Fig. 1 B,C). The highest seed numbers per capsule were obtained under D11 and D19 (Fig. 1 D). Meanwhile, the highest 1000-seed weights were obtained under D11N90 and D19N60 (Fig. 1 E). Collectively, D19N60 was chosen as the most optimal and environmentally friendly condition for improved sesame yield (Fig. 1 ). 3.2. Sesame nitrogen use efficiency was significantly improved under the optimal plant density and nitrogen dose N is crucial for sesame growth and yield (Zenawi & Mizan, 2019b ). To delve into the impacts of different PDs and N doses on sesame NUE, we first evaluated total dry matter, N accumulation, biomass allocation to organs, and N allocation to organs (Figs. 2 and 3 ). All these traits were affected by both PD and N dose (Figs. 2 and 3 ). Under the same PD, the total dry matter and N accumulation significantly increased with the N rate, except for PD of 190,000 plants·hm − 2 (Figs. 2 A,B). Notably, under D19, the total dry matter and N accumulation significantly increased and then decreased, with the maximal values recorded at N dose of 60 kg·hm − 2 (Figs. 2 A,B). D19N60 yielded the highest total dry matter and N accumulation (Figs. 2 A,B). In contrast to seeds, the biomass allocation to leaves and stems increased with the increase in N application rate (Fig. 3 A). Nitrogen accumulated more in sesame seeds than in other organs (Fig. 3 B). The nitrogen allocated to seeds increased with the PD and decreased with the increase in N dose (Fig. 3 B). High PD and low N-dose promoted nitrogen accumulation in seeds ( Fig. 3 B ) . The highest nitrogen allocation rates to seeds of 73 and 74% were recorded under D19N60 and D19N30, respectively ( Fig. 3 B ) . Under the optimal condition of D19N60, the biomass allocated to seed, shell, stem, and leaves was 30%, 30%, 34%, and 6%, respectively ( Fig. 3 B ) . Next, we investigated the effects of different N doses and PDs on NUE, nitrogen uptake efficiency (NUpE), nitrogen utilization efficiency (NUtE), and agronomic efficiency of nitrogen fertilizer (AEN). As presented in Fig. 4 , both N use characteristics were significantly influenced by PD and N rates. The NUE, NUpE, NUtE, and AEN significantly decreased with the increase in N dose, except under D19 (Fig. 4 A-D). NUE significantly increased and then decreased under the PD of 190,000 plants·hm − 2 , with the highest NUE (1.46 ± 0.07%) recorded at N dose of 60 kg·hm − 2 (Fig. 4 A). 3.3. Planting densities and N doses dramatically impact sesame seed oil, protein, and fatty acid (FA) composition Oil content (OC), protein content (PC), and FA composition are key quality characteristics of sesame seeds. Under the same PD, the OC significantly decreased with increased N doses (Table 1 ). In contrast, the PC significantly increased along with the increase in N doses (Table 1 ). Regarding the PD, the OC showed an increased tendency, while the PC decreased with increased PD (Table 1 ). The sesame seed FA profile was significantly influenced by the PD and the N dose (Table 1 ). SFA (saturated fatty acid) content significantly increased with the increase in N dose, while UFA (unsaturated fatty acid) content decreased significantly (Table 1 ). The decrease in UFA content is attributed to reduced linoleic acid content under low-density conditions or decreased oleic acid content under high PD conditions (Table 1 ). The OC, PC, SFA, and UFA content of seeds under the optimal conditions was 50.11 ± 0.45%, 23.78 ± 0.45%, 14.7 ± 0.19%, and 85.01 ± 0.34%, respectively (Table 1 ), which are in the range of high-quality sesame seeds. Meanwhile, the oleic acid, linoleic acid, palmitic acid, and stearic acid content of seeds was 36.68 ± 0.69%, 47.69 ± 0.88%, 8.99 ± 0.01%, and 4.83 ± 0.18%, respectively (Table 1 ). Table 1 Effects of density and nitrogen application rate on sesame seed quality traits Treatment Fat (%) Protein (%) SFA (%) UFA (%) Oleic acid (%) Linoleic acid (%) Palmitic acid (%) Stearic acid (%) D11N0 52.99 ± 0.58 a 19.56 ± 1.06 c 14.44 ± 0.15 c 86.11 ± 0.33 a 36.06 ± 0.59 a 49.41 ± 0.86 a 8.99 ± 0.01 a 4.6 ± 0.14 c D11N30 50.12 ± 0.29 b 23.4 ± 1.35 b 14.73 ± 0.15 b 85.17 ± 0.16 b 36.86 ± 0.52 a 47.67 ± 0.54 bc 8.99 ± 0.01 a 4.85 ± 0.14 b D11N60 49.65 ± 0.5 bc 24.47 ± 0.94 a 14.64 ± 0.1 b 85.06 ± 0.28 b 36.15 ± 1.29 a 48.27 ± 1.23 b 8.99 ± 0.01 a 4.75 ± 0.07 b D11N90 49.63 ± 0.06 bc 25.6 ± 1.06 a 14.67 ± 0.22 b 84.99 ± 0.47 b 36.11 ± 0.76 a 48.24 ± 0.77 b 9 ± 0.02 a 4.77 ± 0.2 b D11N120 49.45 ± 0.29 c 25.27 ± 0.41 a 14.91 ± 0.06 a 84.6 ± 0.28 c 36.81 ± 0.39 a 47.15 ± 0.6 c 8.98 ± 0.02 a 5.02 ± 0.08 a D15N0 49.27 ± 0.55 a 21.39 ± 0.36 c 14.2 ± 0.11 c 86.55 ± 0.09 a 40.47 ± 1.94 a 45.04 ± 1.91 a 8.7 ± 0.05 a 4.72 ± 0.03 a D15N40 48.76 ± 0.39 a 23.72 ± 0.66 b 14.33 ± 0.02 b 86.44 ± 0.05 b 41.55 ± 0.65 a 43.9 ± 0.53 a 8.68 ± 0.07 a 4.67 ± 0.07 a D15N80 47.46 ± 0.34 b 24.65 ± 0.31 a 14.43 ± 0.07 b 86 ± 0.04 c 42.12 ± 0.65 a 43.49 ± 0.84 a 8.77 ± 0.34 a 4.68 ± 0.1 a D15N120 47.63 ± 0.37 b 24.98 ± 0.2 a 14.57 ± 0.03 a 85.98 ± 0.1 c 42.2 ± 0.41 a 43.62 ± 0.34 a 8.92 ± 0.17 a 4.66 ± 0.06 a D19N0 53.34 ± 0.67 a 19.84 ± 1.79 c 14.35 ± 0.28 b 86.19 ± 0.37 a 37.3 ± 0.41 a 48.26 ± 0.69 a 8.99 ± 0.01 a 4.52 ± 0.26 b D19N30 51.85 ± 1.47 b 21.97 ± 2.04 b 14.57 ± 0.16 a 85.46 ± 0.55 b 36.75 ± 0.64 ab 48.08 ± 0.97 a 8.98 ± 0.02 a 4.74 ± 0.16 a D19N60 50.11 ± 0.45 c 23.78 ± 0.45 a 14.7 ± 0.19 a 85.01 ± 0.34 c 36.68 ± 0.69 ab 47.69 ± 0.88 a 8.99 ± 0.01 a 4.83 ± 0.18 a D19N90 50.01 ± 0.56 c 24.54 ± 1.05 a 14.74 ± 0.15 a 84.76 ± 0.3 c 36.25 ± 1.21 bc 47.86 ± 1.22 a 8.99 ± 0.02 a 4.85 ± 0.14 a D19N120 50.22 ± 0.24 c 24.34 ± 0.57 a 14.68 ± 0.23 a 85.08 ± 0.34 c 35.94 ± 0.35 c 48.51 ± 0.6 a 8.97 ± 0.02 a 4.82 ± 0.22 a D25N0 49.76 ± 0.46 a 21.12 ± 0.41 c 14.25 ± 0.02 c 86.46 ± 0.07 a 40.61 ± 1.2 a 44.65 ± 1.15 a 8.63 ± 0.08 b 4.74 ± 0.06 a D25N40 49.42 ± 0.1 a 22.89 ± 0.31 b 14.32 ± 0.01 b 86.26 ± 0.07 b 41.53 ± 0.8 a 43.97 ± 1 a 8.71 ± 0.03 ab 4.72 ± 0.04 a D25N80 48.47 ± 0.07 b 23.47 ± 0.47 ab 14.34 ± 0 b 86.09 ± 0.03 c 41.23 ± 0.74 a 44.1 ± 0.55 a 8.8 ± 0.09 a 4.7 ± 0.01 a D25N120 48.05 ± 0.31 b 23.69 ± 0.55 a 14.41 ± 0.06 a 86.03 ± 0.11 c 41.88 ± 1.17 a 43.79 ± 1.25 a 8.76 ± 0.07 a 4.63 ± 0.02 b D41N0 50.71 ± 0.21 a 20.85 ± 0.18 c 14.28 ± 0.01 c 86.13 ± 0.06 a 41.67 ± 0.67 a 45.46 ± 0.65 a 8.69 ± 0.11 c 4.71 ± 0.09 a D41N40 49.71 ± 0.28 b 21.68 ± 0.61 b 14.35 ± 0.02 b 85.96 ± 0.06 b 41.71 ± 0.44 a 43.42 ± 0.44 c 8.71 ± 0.06 b 4.72 ± 0.03 a D41N80 49.78 ± 0.32 b 23.27 ± 0.83 a 14.37 ± 0.01 b 85.82 ± 0.03 c 40.34 ± 0.41 b 45.09 ± 0.35 a 8.89 ± 0.09 a 4.72 ± 0.02 a D41N120 49.9 ± 0.24 b 23.68 ± 0.41 a 14.48 ± 0.07 a 85.79 ± 0.08 c 40.88 ± 0.3 b 44.26 ± 0.36 b 8.84 ± 0.08 a 4.65 ± 0.07 a N ** ** ** ** ** ** ** ns D ** ** ** ** ** ** ** ns N*D ** ** * ** ** ** ** ** Note : D11, D15, D19, D25, and D41 indicate different densities. N…, different nitrogen application rates. Lowercase letters show differences under the same density with different nitrogen application ratios. Uppercase letters indicate differences under the same nitrogen application with different densities. *, ** indicate significance at P ˂ 0.05 and 0.01, respectively. ns, no significance. 3.4. Correlations between traits, density, and nitrogen rates To better understand the relationships between PD or N-dose and sesame yield and quality components, we conducted a correlation analysis. As shown in Fig. 5 , PD was significantly and negatively correlated with the number of capsules (r = -0.89), the number of seeds per capsule (r = -0.72), the 1000-seeds weight (r= -0.64), PC (r = -0.60), and linoleic acid content (r= -0.50) (Fig. 5 ). Nitrogen application rate was significantly and positively correlated with PC (r = 0.63), total biomass (r = 0.63), and total N content (r = 0.65) (Fig. 5 ). In contrast, the nitrogen application rate was significantly and negatively correlated with NUE (r = -0.69), NUpE (r = -0.91), and AEN (r = -0.65) (Fig. 5 ). PD is positively correlated with oleic acid content (r = 0.49). Oleic acid was significantly and negatively correlated with linoleic acid (r = -0.99), palmitic acid (r = -0.87), and stearic acid (r = -0.74). NUE was significantly and positively correlated with NUpE (r = 0.77) and AEN (r = 0.90) (Fig. 5 ). A negative correlation (r = -0.41) was recorded between OC and PC. 3.5. Prediction of yield for different nitrogen doses and planting densities To facilitate the use of optimum N-dose for maximum yield under different PDs, we predicted regression equations for the grain yields (Table 2 ). It is expected that 190,000 plants·hm − 2 PD and 76.6366 kg·hm − 2 nitrogen rate would yield a maximum of 2627.0327 kg·hm − 2 sesame seeds (Table 2 ). Table 2 Regression equations for the effect of the N rate at different planting densities Density Regression equation r 2 Predicted extremum (kg·hm − 2 ) Suitable amount of nitrogen (kg·hm − 2 ) D11 Y = 1016.8734 + 22.1670x − 0.1096x 2 0.9900 2137.6075 101.1411 D19 Y = 1701.4325 + 24.1572x − 0.1576x 2 0.8902 2627.0327 76.6366 D15 Y = 985.4284 + 9.2000x − 0.0134x 2 0.9332 1896.5669 120 D25 Y = 1163.9645 + 20.6522x − 0.0970x 2 0.9983 2263.4646 106.42643 D41 Y = 1332.2283 + 8.2989x − 0.0248x 2 0.9977 1971.0724 120 4. Discussion Currently, higher production of sesame causes considerable environmental risks due to excessive use of fertilizers. For instance, studies have demonstrated that high sesame yields can be achieved with 120 kg·hm − 2 N-dose (李亚贞 et al., 2015; 王龙 et al., 2022). Due to climate change, sustainability, and health purposes, it is essential to develop strategies to maximize sesame yield under reduced N application rates. The low branching ability of sesame made the crop suitable for PD. Fortunately, it was found that yield is closely related to capsule numbers in sesame, and capsule numbers per unit area increased significantly with PD (Ramazani, 2016 ). Another study revealed that increasing PD coupled with reduced N rate significantly improves crop yield and resource utilization (Duan et al., 2023 ). In this study, we identified the optimal PD of 190,000 plants·hm − 2 and an N application rate of 60 kg·hm − 2 for maximizing sesame YPUA. Notably, the highest yield was 2690.02 kg·hm − 2 under PD of 190,000 plants·hm − 2 and nitrogen rate of 60 kg·hm − 2 , which was a 50% reduction in the actual recommended N rate and a 26.82% yield increment compared to the control (null nitrogen). Significant increases in biomass and nitrogen accumulation were also recorded under these optimal rates. The highest NUE of 1.46 ± 0.07% was achieved under D19N60. These results show that the optimized PD and N rate can be promoted to improve sesame YPUA and simultaneously minimize environmental pollution risk and potential health concerns due to N loss. The increase in sesame YPUA, coupled with reduced N input, may significantly improve the incomes of smallholder sesame farmers. Extremely dense planting led to a significant reduction in yield and NUE. These results indicate that increased PD causes competition for nutrients, water, and light among sesame plants. The light deficiency may have caused a significant reduction in photosynthesis efficiency and, ultimately, weak anabolism and decreased yields. A previous study showed that the proportion of stems increased with the increase in PD (Duan et al., 2023 ; Postma et al., 2021 ), which was consistent with the results of our experiments. At the same time, the dry matter and N accumulation of stems, leaves, and shells increased with the increase in N application rate, which may be the main reason for the low NUE under high N rate conditions. As support, the N application rate was significantly and negatively correlated with NUE, NUpE, and AEN, while PD was significantly negatively correlated with yield components. PC, OC, and FA composition are critical quality traits in sesame (Wei et al., 2022 ). The OC and PC of sesame seeds are significantly and negatively correlated (Li et al., 2014 ). Herein, we also recorded a negative correlation between OC and PC. The PC significantly increased with the increase in N application rate and decreased with the increase in PD. In contrast, the OC significantly dropped with increased N rates, but the reduction was less with increased PD. These results support the statement of enhanced competition for nutrients and light under extremely dense planting. The PD and N rates significantly affected the FA profile of sesame seeds. The reduction in OC, coupled with the alteration of FA composition and the increase in PC, along with the N rate increase, could be explained by enhanced N assimilation processes under high N rate conditions, which led to a reduced allocation of intermediate metabolic resources required for the synthesis of oil body. For instance, in soft wheat, it was found that reduced N rate and PD modify the supply of free amino acid to protein synthesis and the expression of the storage protein gene (B. Zheng et al., 2022 ). Also, pyruvate kinase and phosphoenol pyruvate carboxylase play a central role in modulating N assimilation and amino acid biosynthesis, ATP production via oxidative phosphorylation, and plastidial fatty acid synthesis. The proportion of UFA was increased by reducing the N application rate, which is consistent with reports in other plants (Nosheen et al., 2019 ; Sharifi, Namvar, & Seyed-Sharifi, 2017 ). Taken together, the results show that appropriate PD combined with a reduced amount of N supply may minimize environmental pollution risks and ensure improved yield and seed quality in sesame. Similar cultivation indications have been recommended in soft wheat to guarantee high yields and satisfactory grain quality (B. Zheng et al., 2022 ). We have provided regression equations that may facilitate the optimization of PD and N rates according to needs. The optimal PD of 190,000 plants·hm − 2 and N application rate of 60 kg·hm − 2 identified in this study should be further tested in different environments and on different soils for validation before being promoted. 5. Conclusions Overall, the yield and quality characteristics of sesame were analyzed under different N and PD conditions in this study. We found that an optimal PD of 190,000 plants·hm − 2 coupled with an N application rate of 60 kg·hm − 2 could be applied for improving sesame yield, biomass, NUE, nitrogen allocation to seeds, and seed quality traits, including PC, FA composition, and oil content. Higher N-dose improved seed PC but significantly reduced NUE, OC, and UFA content. Correlations between PD/N rate and NUE, yield and quality traits are revealed. Our results will guide the sustainable and environmentally friendly enhancement of sesame NUE, production, and quality. Declarations Funding This study was funded by the Key Development Program Project in Jiangxi Province (20243BBH81029), Jiangxi Agriculture Research System (JXARS-18), and the Sesame Seed Joint Research Project of Jiangxi Province. Data availability The data that support the findings of this study are available from the corresponding author upon reasonable request. Author Information Affiliation: Key Laboratory of Crop Physiology, Ecology, and Genetic Breeding, Ministry of Education/College of Agronomy, Jiangxi Agricultural University, Nanchang 330045, China. Correspond ing author : Ziming Wu, [email protected] . Authors' contribution: M.W., Z.W., and S.F. designed the experiment. M.W. performed the experiments. X.W., G.W., H.Y., T.S., and Z.W. participated in conducting the experiment. X.Y. contributed to the seed quality analyses. M.W. analyzed the data and wrote the draft. Z.W. reviewed the final manuscript. All authors read and approved the final manuscript. Ethics Declarations Conflicts of Interest The authors declare no competing interests. References Basso, B., Cammarano, D., Troccoli, A., Chen, D., & Ritchie, J. T. (2010). Long-term wheat response to nitrogen in a rainfed Mediterranean environment: Field data and simulation analysis. 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International Journal of Agronomy, 2019 (1), 5027254. doi:https://doi.org/10.1155/2019/5027254 Zenawi, G., & Mizan, A. (2019b). Effect of Nitrogen Fertilization on the Growth and Seed Yield of Sesame ( Sesamum indicum L.). International Journal of Agronomy , 1-7. Zhao, W., Ren, T. H., Huang, X. Y., Xu, Z., Zhou, Y. Z., Yin, C. L., Zhao, R., Liu, S.B., Ning, T.Y. & Li, G. (2023). Leaf shape, planting density, and nitrogen application affect soybean yield by changing direct and diffuse light distribution in the canopy. Plant Physiol Biochem, 204 , 108071. doi:10.1016/j.plaphy.2023.108071 Zheng, B., Fang, Q., Zhang, C., Mahmood, H., Zhou, Q., Li, W., Li, X., Cai, J., Wang, X., Zhong, Y., Huang, M., Cao, W., Dai, T. & Jiang, D. (2020). Reducing nitrogen rate and increasing plant density benefit processing quality by modifying the spatial distribution of protein bodies and gluten proteins in endosperm of a soft wheat cultivar. Field Crops Research, 253 . doi:10.1016/j.fcr.2020.107831 Zheng, B., Jiang, J., Wang, L., Huang, M., Zhou, Q., Cai, J., Wang, X., Dai, T., Jiang, D. (2022). Reducing Nitrogen Rate and Increasing Plant Density Accomplished High Yields with Satisfied Grain Quality of Soft Wheat via Modifying the Free Amino Acid Supply and Storage Protein Gene Expression. J Agric Food Chem, 70 (7), 2146-2159. doi:10.1021/acs.jafc.1c07033 Zhi, X.Y., Han, Y.C., Li, Y.B., Wang, G.P., Du, W., Li, X.X., Mao, S., Feng, L. (2016). Effects of plant density on cotton yield components and quality. Journal of Integrative Agriculture, 15 (7), 1469-1479. doi:https://doi.org/10.1016/S2095-3119(15)61174-1 Additional Declarations No competing interests reported. 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14:09:31","extension":"xml","order_by":31,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":114581,"visible":true,"origin":"","legend":"","description":"","filename":"04dd090d07a34afeb38147e1e5a401541structuring.xml","url":"https://assets-eu.researchsquare.com/files/rs-8083903/v1/b4362e7537f730de903e5016.xml"},{"id":96822168,"identity":"ab2cc0a3-5927-45cd-b9cb-953900bcb9d7","added_by":"auto","created_at":"2025-11-26 12:12:06","extension":"html","order_by":32,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":121665,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-8083903/v1/0461dcc8e340e979eb5f916a.html"},{"id":96916779,"identity":"afc9aa26-ae77-4552-937a-0226d2ac58e2","added_by":"auto","created_at":"2025-11-27 14:08:52","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":157268,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eImpacts of different planting densities and nitrogen doses on sesame yield and yield components.\u003c/strong\u003e (A) Seed yield. (B) Seed weight. (C) Number of capsules per plant. (D) Seed number per capsule. (E) Thousand seed weight. D11, D15, D19, D25, and D41 indicate planting density of 110,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 150,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 190,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 250,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, and 410,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, respectively. Different letters indicate statistical differences at \u003cem\u003eP\u003c/em\u003e ˂ 0.05. D, density effect; N, nitrogen effect; D*N, density and nitrogen effects. *, ** indicate significance at \u003cem\u003eP\u003c/em\u003e ˂ 0.05 and 0.01, respectively. ns, no significance.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8083903/v1/ff21c11e7b74704c474306ef.png"},{"id":96822129,"identity":"96c0f638-551f-4e80-b6ef-96d79f785fb5","added_by":"auto","created_at":"2025-11-26 12:12:05","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":116958,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eImpacts of different planting densities and nitrogen doses on biomass and nitrogen accumulation in sesame.\u003c/strong\u003e (A) Total biomass at harvest. (B) Nitrogen accumulation of sesame. D11, D15, D19, D25, and D41 indicate planting density of 110,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 150,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 190,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 250,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, and 410,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, respectively. Different letters indicate statistical differences at \u003cem\u003eP\u003c/em\u003e ˂ 0.05. D, density effect; N, nitrogen effect; D*N, density and nitrogen effects. *, ** indicate significance at \u003cem\u003eP\u003c/em\u003e ˂ 0.05 and 0.01, respectively. ns, no significance.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8083903/v1/45395a1c52f59b5904d97b20.png"},{"id":96822137,"identity":"202a4f16-5392-4551-9d0b-238364c1fe35","added_by":"auto","created_at":"2025-11-26 12:12:05","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":335759,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eImpacts of different planting densities and nitrogen doses on biomass allocation and nitrogen allocation to sesame tissues.\u003c/strong\u003e (A) Biomass allocated to sesame tissues. (B) Nitrogen allocated to sesame tissues. D11, D15, D19, D25, and D41 indicate planting density of 110,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 150,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 190,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 250,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, and 410,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, respectively. Different letters indicate statistical differences at \u003cem\u003eP\u003c/em\u003e ˂ 0.05. D, density effect; N, nitrogen effect; D*N, density and nitrogen effects. *, ** indicate significance at \u003cem\u003eP\u003c/em\u003e ˂ 0.05 and 0.01, respectively. ns, no significance.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8083903/v1/223b2f1a5ec5d29841d5dcc7.png"},{"id":96822134,"identity":"35d9347c-43d5-407c-bd21-0ba71ac505fc","added_by":"auto","created_at":"2025-11-26 12:12:05","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":150120,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eImpacts of different planting densities and nitrogen doses on sesame nitrogen use efficiency (NUE).\u003c/strong\u003e (A) NUE. (B) NUpE, nitrogen uptake efficiency. (C) NUtE, nitrogen utilization efficiency. (D) AEN, agronomic efficiency of nitrogen fertilizer. D11, D15, D19, D25, and D41 indicate planting density of 110,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 150,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 190,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, 250,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, and 410,000 plants·hm\u003csup\u003e-2\u003c/sup\u003e, respectively. Different letters indicate statistical differences at \u003cem\u003eP\u003c/em\u003e ˂ 0.05. D, density effect; N, nitrogen effect; D*N, density and nitrogen effects. *, ** indicate significance at \u003cem\u003eP\u003c/em\u003e ˂ 0.05 and 0.01, respectively. ns, no significance.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8083903/v1/dea050fcd72848020bedabd0.png"},{"id":96918022,"identity":"96c023df-d1fd-419f-a399-8f5e2e5320fa","added_by":"auto","created_at":"2025-11-27 14:11:01","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":307553,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCorrelation matrix between the planting density (D), nitrogen rate (N), and the different evaluated traits, including yield, quality, and N use components.\u003c/strong\u003e CPP, capsules number per plant; SPC, seeds number per capsule; 1000-SW, thou sand seeds weight; SY, seed yield; F, fat content; P, protein content; OA, oleic acid; LA, linoleic acid; PA, palmitic acid; SA, stearic acid; TBA, total biomass accumulation; TNA, total nitrogen accumulation; NUE, nitrogen use efficiency; NUpE, nitrogen uptake efficiency; NUtE, nitrogen utilization efficiency; AEN, agronomic efficiency of nitrogen fertilizer\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8083903/v1/986bc08f75d66dae581bfb2e.png"},{"id":102422972,"identity":"39572765-25ba-4c35-a122-ff69e8ab0c76","added_by":"auto","created_at":"2026-02-11 13:58:47","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2194057,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8083903/v1/4b7ed810-fb9b-4aea-9d19-aba839897fa9.pdf"},{"id":96918349,"identity":"411eee7f-0ea4-4382-9b6f-22618a571f78","added_by":"auto","created_at":"2025-11-27 14:11:49","extension":"pdf","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":120592,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementaryfigures.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8083903/v1/2bd916698395cd07e53817b7.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Optimizing planting density and nitrogen input for improved nitrogen use efficiency, yield and seed quality in sesame","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eHigher crop yield per unit area (YPUA) is crucial to guarantee food security. Among the factors that influence crops\u0026rsquo; YPUA include principally PD and N supply (Wu et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Zhao et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Sparse planting and a higher N dose can facilitate N availability for plants (Stockmann et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, it is vital to gain a higher yield through the group effect (Hou et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Huang, Chen, Cao, \u0026amp; Zou, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Zhi et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Accordingly, studies revealed that increasing PD combined with an appropriate N dose significantly improves crop yield (Duan, Wei, Soualiou, \u0026amp; Zhou, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). Dense planting coupled with reduced N dose is one of the key strategies in green agricultural production (Basso, Cammarano, Troccoli, Chen, \u0026amp; Ritchie, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2010\u003c/span\u003e). Unfortunately, PD and N doses have not yet been optimized for major nutritional crops, limiting efforts to mitigate environmental risks associated with intensive agricultural practices.\u003c/p\u003e\u003cp\u003eSesame is an important cash crop for smallholder farmers in growing countries (Dossa, Konteye, Niang, Doumbia, \u0026amp; Ciss\u0026eacute;, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Of the different sesame types, black sesame presents the most health benefits, nutritional values, and food industrial applications (Xu et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In upland hilly red soil regions of southern China, black sesame is of higher economic value for smallholders. Unfortunately, in the past 10 years, the YPUA of black sesame has been increasing slowly, while the available arable land is decreasing significantly. Farmers often apply more N fertilizer to improve seed yield (Kalaiselvan P., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). For instance, in China, some farmers plant sesame at extremely wide spacing, and they think that the low density with high N nutrition can make sesame plants strong and produce more capsules. Yet, limited research was conducted to support this ecotoxic statement. High N application rates often lead to nitrogen loss, causing environmental pollution and food security concerns (Wang, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Researchers have recently found that yield is closely related to capsule numbers in sesame, and capsule numbers per unit area increased significantly with PD (Ramazani, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Increased density causes competition for nutrition, water, and light among plants. However, the dry matter and leaf area index of sesame increased significantly under dense planting conditions. Thus, PD and N input rates are critical factors influencing sesame yields (Rui-qing et al., 2017; Zenawi \u0026amp; Mizan, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2019a\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019b\u003c/span\u003e). However, still less is known regarding the combined effects of these two factors on yields and seed quality in sesame.\u003c/p\u003e\u003cp\u003eStudies have shown that high N rates increase the protein content of crop grains but reduce the levels of secondary metabolites and certain nutrients (Khan et al., \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Mostashari \u0026amp; Mousavi Khaneghah, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Baoqiang Zheng et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Sesame is a nutrient-rich and functional food highly appreciated for its quality value (Deme, Narasimhulu, \u0026amp; Parthasarathy, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Its seeds comprise 45\u0026thinsp;~\u0026thinsp;65% oil, 19\u0026thinsp;~\u0026thinsp;35% protein, and 14\u0026thinsp;~\u0026thinsp;20% carbohydrates (Mostashari \u0026amp; Mousavi Khaneghah, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Xu et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Sesame seed oils are rich sources of unsaturated fatty acids (UFA) (mainly 35.9\u0026thinsp;~\u0026thinsp;42.3% oleic acid and 41.5\u0026thinsp;~\u0026thinsp;47.9% linoleic acid). The saturated fatty acids (SFA) (palmitic acid 7.9\u0026thinsp;~\u0026thinsp;12% and stearic acid 4.8\u0026thinsp;~\u0026thinsp;6.1%) represent less than 20% (Mostashari \u0026amp; Mousavi Khaneghah, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Xu et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Cultivating nutrient-rich and high-yielding sesame varieties is one of the major breeding goals. Hence, it is vital to determine an optimal PD and N application rate to improve the sustainable production of high-quality sesame seeds. Sustainable measures are the best approaches to enhance crop-derived products\u0026rsquo; quality and quantity for human consumption (Nosheen et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eIn the present study, we investigated the combined effects of PD and N application rates on sesame NUE, yield, and quality components in the field under a hilly red soil region in southern China. We aimed to determine an optimal PD and N rate for increasing sesame NUE, YPUA, and quality.\u003c/p\u003e"},{"header":"2. Methods and Materials","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Experimental design\u003c/h2\u003e\u003cp\u003eField experiments were conducted in 2022 at the Jiangxi Agriculture University (28.45\u0026deg;N, 1115.49\u0026deg;E, 78 m altitude), Jiangxi Province, China. The site is located in a subtropical monsoon climate zone and a hilly red soil region in southern China. The soil characteristics were as follow: pH\u0026thinsp;=\u0026thinsp;4.73, organic matter\u0026thinsp;=\u0026thinsp;15.51 g\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, total N\u0026thinsp;=\u0026thinsp;0.13%, available nitrogen N\u0026thinsp;=\u0026thinsp;102.66 mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, available P\u0026thinsp;=\u0026thinsp;31.49 mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, available K\u0026thinsp;=\u0026thinsp;148.48 mg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Average daily temperatures (minimum and maximum) and rainfall during the experiment period are shown in \u003cb\u003eFigure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e.\u003c/p\u003e\u003cp\u003eA black sesame cultivar, \u0026lsquo;Jinhuangma\u0026rsquo; was used in this experiment. It has been adopted by farmers due to its high yield and palatability. The trial was designed using a randomized block design with four replications, considering two factors: different N application rates and different PDs. N fertilizer was applied as urea at 0, 30, 40, 60, 80, 90, and 120 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (labeled N0, N30, N40, N60, N80, N90, and N120, respectively). PDs were 110,000, 150,000, 190,000, 250,000, and 410,000 plants\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (termed D11, D15, N19, D25, and D41, respectively). The plot size was 16 m\u003csup\u003e2\u003c/sup\u003e (4 m \u0026times; 4 m). The plots were distanced by 0.5 m to prevent cross-contamination and treatment effects. When 2\u0026ndash;3 pairs of leaves grew, the seedlings were thinned according to the corresponding density. Phosphate (P₂O₅) and potassium (K₂O) fertilizers were applied (sprinkled before sowing) once as a basal at the rate of 50 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 100 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Grain yield, yield components, and biomass\u003c/h2\u003e\u003cp\u003eThree evenly grown plants were chosen from each plot and harvested when they were fully mature. The 1000-grain weight, the seed number per capsule, and the number of capsules per plant were counted. Stems, leaves, flowers, shells, and seeds were dried at 105\u0026deg;C for 30 min, followed by 70\u0026deg;C for 72 h, and then weighed. The total dry matter accumulated\u0026thinsp;=\u0026thinsp;the sum of the dry weights of each component.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3. Nitrogen uptake\u003c/h2\u003e\u003cp\u003eThe dry matter was ground into powder and used to determine N content in each tissue using the Kjeldahl method. Nitrogen accumulation in each tissue was calculated as N content multiplied by the dry matter accumulation. Total nitrogen accumulation of the whole plant is the sum of the N accumulated in each tissue.\u003c/p\u003e\u003cp\u003eNitrogen use efficiency (NUE, %) = (N accumulation in plants at maturity under N application - N accumulation in plants at maturity under control) / N rates\u0026times;100\u003c/p\u003e\u003cp\u003eN uptake efficiency (NUpE, kg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u0026thinsp;=\u0026thinsp;Total N accumulated in plants / N rates\u003c/p\u003e\u003cp\u003eN utilization efficiency (NUtE, kg\u0026middot;kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u0026thinsp;=\u0026thinsp;Yield/ Total N accumulated in plants\u003c/p\u003e\u003cp\u003eAgronomic efficiency of N fertilizer (AEN, %) = (Yield under N application - Yield under control) / N rates\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4. Oil content, fatty acid composition, and protein content\u003c/h2\u003e\u003cp\u003eOils, fatty acid composition, and protein content were determined using near-infrared spectroscopy (严圭 et al., 2020). The seeds were harvested at maturity, and samples were detected by a DS2500F-type near-infrared spectrometer (Foss, USA) and repeated three times.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5. Data analysis\u003c/h2\u003e\u003cp\u003eAll statistical analyses were performed using IBM SPSS Statistics 24 (SPSS Inc., USA). Mean differences were determined using the Duncan test at \u003cem\u003eP\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05. Figures were generated using Origin 2021 software.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.1. Optimal plant density and nitrogen dose for higher sesame seed yield per unit area\u003c/h2\u003e\u003cp\u003eTo identify an optimal N rate and PD for maximizing sesame YPUA, the black sesame cultivar \u0026lsquo;Jinhuangma\u0026rsquo; was cultivated under different N doses and PDs. We found that both nitrogen rates and PD significantly affected seed yield and yield components \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA-E\u003cb\u003e)\u003c/b\u003e. Under the same PD, the yield, seed weight per plant, capsule number per plant, seed number per capsule, and thousand-seed weight increased significantly with the N dose, then stabilized from an N rate of 60 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA-E). The best yield performances were obtained at the PD of 190,000 plants\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, with the highest yield recorded for an N dose of 60 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (D19N60) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). Under the same N dose, seed weight and number of capsules per plant decreased significantly with the increase in PD (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB,C). The highest seed numbers per capsule were obtained under D11 and D19 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD). Meanwhile, the highest 1000-seed weights were obtained under D11N90 and D19N60 (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eE). Collectively, D19N60 was chosen as the most optimal and environmentally friendly condition for improved sesame yield (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Sesame nitrogen use efficiency was significantly improved under the optimal plant density and nitrogen dose\u003c/h2\u003e\u003cp\u003eN is crucial for sesame growth and yield (Zenawi \u0026amp; Mizan, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019b\u003c/span\u003e). To delve into the impacts of different PDs and N doses on sesame NUE, we first evaluated total dry matter, N accumulation, biomass allocation to organs, and N allocation to organs (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). All these traits were affected by both PD and N dose (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). Under the same PD, the total dry matter and N accumulation significantly increased with the N rate, except for PD of 190,000 plants\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA,B). Notably, under D19, the total dry matter and N accumulation significantly increased and then decreased, with the maximal values recorded at N dose of 60 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA,B). D19N60 yielded the highest total dry matter and N accumulation (Figs.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA,B).\u003c/p\u003e\u003cp\u003eIn contrast to seeds, the biomass allocation to leaves and stems increased with the increase in N application rate (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA). Nitrogen accumulated more in sesame seeds than in other organs (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). The nitrogen allocated to seeds increased with the PD and decreased with the increase in N dose (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB). High PD and low N-dose promoted nitrogen accumulation in seeds \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB\u003cb\u003e)\u003c/b\u003e. The highest nitrogen allocation rates to seeds of 73 and 74% were recorded under D19N60 and D19N30, respectively \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB\u003cb\u003e)\u003c/b\u003e. Under the optimal condition of D19N60, the biomass allocated to seed, shell, stem, and leaves was 30%, 30%, 34%, and 6%, respectively \u003cb\u003e(\u003c/b\u003eFig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB\u003cb\u003e)\u003c/b\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eNext, we investigated the effects of different N doses and PDs on NUE, nitrogen uptake efficiency (NUpE), nitrogen utilization efficiency (NUtE), and agronomic efficiency of nitrogen fertilizer (AEN). As presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, both N use characteristics were significantly influenced by PD and N rates. The NUE, NUpE, NUtE, and AEN significantly decreased with the increase in N dose, except under D19 (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA-D). NUE significantly increased and then decreased under the PD of 190,000 plants\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, with the highest NUE (1.46\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07%) recorded at N dose of 60 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003e3.3. Planting densities and N doses dramatically impact sesame seed oil, protein, and fatty acid (FA) composition\u003c/b\u003e\u003c/p\u003e\u003cp\u003eOil content (OC), protein content (PC), and FA composition are key quality characteristics of sesame seeds. Under the same PD, the OC significantly decreased with increased N doses (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In contrast, the PC significantly increased along with the increase in N doses (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Regarding the PD, the OC showed an increased tendency, while the PC decreased with increased PD (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The sesame seed FA profile was significantly influenced by the PD and the N dose (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). SFA (saturated fatty acid) content significantly increased with the increase in N dose, while UFA (unsaturated fatty acid) content decreased significantly (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The decrease in UFA content is attributed to reduced linoleic acid content under low-density conditions or decreased oleic acid content under high PD conditions (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The OC, PC, SFA, and UFA content of seeds under the optimal conditions was 50.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.45%, 23.78\u0026thinsp;\u0026plusmn;\u0026thinsp;0.45%, 14.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.19%, and 85.01\u0026thinsp;\u0026plusmn;\u0026thinsp;0.34%, respectively (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), which are in the range of high-quality sesame seeds. Meanwhile, the oleic acid, linoleic acid, palmitic acid, and stearic acid content of seeds was 36.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.69%, 47.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.88%, 8.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01%, and 4.83\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18%, respectively (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\u003eEffects of density and nitrogen application rate on sesame seed quality traits\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"9\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\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\u003eFat (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eProtein (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eSFA (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eUFA (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eOleic acid (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eLinoleic acid (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003ePalmitic acid (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eStearic acid (%)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD11N0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e52.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.58 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e19.56\u0026thinsp;\u0026plusmn;\u0026thinsp;1.06 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.44\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e86.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.33 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e36.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.59 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e49.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.86 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14 c\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD11N30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e50.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23.4\u0026thinsp;\u0026plusmn;\u0026thinsp;1.35 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e85.17\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e36.86\u0026thinsp;\u0026plusmn;\u0026thinsp;0.52 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e47.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.54 bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14 b\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD11N60\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5 bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e24.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.94 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.64\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e85.06\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e36.15\u0026thinsp;\u0026plusmn;\u0026thinsp;1.29 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e48.27\u0026thinsp;\u0026plusmn;\u0026thinsp;1.23 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07 b\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD11N90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 bc\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e25.6\u0026thinsp;\u0026plusmn;\u0026thinsp;1.06 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e84.99\u0026thinsp;\u0026plusmn;\u0026thinsp;0.47 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e36.11\u0026thinsp;\u0026plusmn;\u0026thinsp;0.76 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e48.24\u0026thinsp;\u0026plusmn;\u0026thinsp;0.77 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.77\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2 b\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD11N120\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.29 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e25.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.41 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.91\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e84.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e36.81\u0026thinsp;\u0026plusmn;\u0026thinsp;0.39 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e47.15\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.98\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e5.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08 a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" 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a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22 a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD25N0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.46 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e21.12\u0026thinsp;\u0026plusmn;\u0026thinsp;0.41 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.25\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e86.46\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e40.61\u0026thinsp;\u0026plusmn;\u0026thinsp;1.2 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e44.65\u0026thinsp;\u0026plusmn;\u0026thinsp;1.15 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.74\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD25N40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e22.89\u0026thinsp;\u0026plusmn;\u0026thinsp;0.31 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.32\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e86.26\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e41.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e43.97\u0026thinsp;\u0026plusmn;\u0026thinsp;1 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03 ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04 a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD25N80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e48.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23.47\u0026thinsp;\u0026plusmn;\u0026thinsp;0.47 ab\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e86.09\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e41.23\u0026thinsp;\u0026plusmn;\u0026thinsp;0.74 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e44.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.55 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD25N120\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e48.05\u0026thinsp;\u0026plusmn;\u0026thinsp;0.31 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.55 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e86.03\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e41.88\u0026thinsp;\u0026plusmn;\u0026thinsp;1.17 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e43.79\u0026thinsp;\u0026plusmn;\u0026thinsp;1.25 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 b\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD41N0\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e50.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e20.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.18 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.28\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e86.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e41.67\u0026thinsp;\u0026plusmn;\u0026thinsp;0.67 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e45.46\u0026thinsp;\u0026plusmn;\u0026thinsp;0.65 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.69\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09 a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD41N40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e21.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.61 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e85.96\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e41.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.44 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e43.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.44 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.71\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03 a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD41N80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49.78\u0026thinsp;\u0026plusmn;\u0026thinsp;0.32 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23.27\u0026thinsp;\u0026plusmn;\u0026thinsp;0.83 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.37\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e85.82\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e40.34\u0026thinsp;\u0026plusmn;\u0026thinsp;0.41 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e45.09\u0026thinsp;\u0026plusmn;\u0026thinsp;0.35 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.89\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02 a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD41N120\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e49.9\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e23.68\u0026thinsp;\u0026plusmn;\u0026thinsp;0.41 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e14.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e85.79\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08 c\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e40.88\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e44.26\u0026thinsp;\u0026plusmn;\u0026thinsp;0.36 b\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e8.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08 a\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e4.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07 a\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eN\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003ens\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003ens\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eN*D\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e*\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e**\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003ctfoot\u003e\u003ctr\u003e\u003ctd colspan=\"9\"\u003e\u003cb\u003eNote\u003c/b\u003e: D11, D15, D19, D25, and D41 indicate different densities. N\u0026hellip;, different nitrogen application rates. Lowercase letters show differences under the same density with different nitrogen application ratios. Uppercase letters indicate differences under the same nitrogen application with different densities. *, ** indicate significance at \u003cem\u003eP\u003c/em\u003e ˂ 0.05 and 0.01, respectively. ns, no significance.\u003c/td\u003e\u003c/tr\u003e\u003c/tfoot\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\u003ch2\u003e3.4. Correlations between traits, density, and nitrogen rates\u003c/h2\u003e\u003cp\u003eTo better understand the relationships between PD or N-dose and sesame yield and quality components, we conducted a correlation analysis. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, PD was significantly and negatively correlated with the number of capsules (r = -0.89), the number of seeds per capsule (r = -0.72), the 1000-seeds weight (r= -0.64), PC (r = -0.60), and linoleic acid content (r= -0.50) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Nitrogen application rate was significantly and positively correlated with PC (r\u0026thinsp;=\u0026thinsp;0.63), total biomass (r\u0026thinsp;=\u0026thinsp;0.63), and total N content (r\u0026thinsp;=\u0026thinsp;0.65) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). In contrast, the nitrogen application rate was significantly and negatively correlated with NUE (r = -0.69), NUpE (r = -0.91), and AEN (r = -0.65) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). PD is positively correlated with oleic acid content (r\u0026thinsp;=\u0026thinsp;0.49). Oleic acid was significantly and negatively correlated with linoleic acid (r = -0.99), palmitic acid (r = -0.87), and stearic acid (r = -0.74). NUE was significantly and positively correlated with NUpE (r\u0026thinsp;=\u0026thinsp;0.77) and AEN (r\u0026thinsp;=\u0026thinsp;0.90) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). A negative correlation (r = -0.41) was recorded between OC and PC.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.5. Prediction of yield for different nitrogen doses and planting densities\u003c/h2\u003e\u003cp\u003eTo facilitate the use of optimum N-dose for maximum yield under different PDs, we predicted regression equations for the grain yields (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). It is expected that 190,000 plants\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e PD and 76.6366 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e nitrogen rate would yield a maximum of 2627.0327 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e sesame seeds (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\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\u003eRegression equations for the effect of the N rate at different planting densities\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDensity\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eRegression equation\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003er\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePredicted extremum (kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eSuitable amount of nitrogen\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\u003eD11\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eY\u0026thinsp;=\u0026thinsp;1016.8734\u0026thinsp;+\u0026thinsp;22.1670x \u0026minus;\u0026thinsp;0.1096x\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.9900\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2137.6075\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e101.1411\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD19\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eY\u0026thinsp;=\u0026thinsp;1701.4325\u0026thinsp;+\u0026thinsp;24.1572x \u0026minus;\u0026thinsp;0.1576x\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.8902\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2627.0327\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e76.6366\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD15\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eY\u0026thinsp;=\u0026thinsp;985.4284\u0026thinsp;+\u0026thinsp;9.2000x \u0026minus;\u0026thinsp;0.0134x\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.9332\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1896.5669\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e120\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD25\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eY\u0026thinsp;=\u0026thinsp;1163.9645\u0026thinsp;+\u0026thinsp;20.6522x \u0026minus;\u0026thinsp;0.0970x\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.9983\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e2263.4646\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e106.42643\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eD41\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003eY\u0026thinsp;=\u0026thinsp;1332.2283\u0026thinsp;+\u0026thinsp;8.2989x \u0026minus;\u0026thinsp;0.0248x\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.9977\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1971.0724\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e120\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eCurrently, higher production of sesame causes considerable environmental risks due to excessive use of fertilizers. For instance, studies have demonstrated that high sesame yields can be achieved with 120 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e N-dose (李亚贞 et al., 2015; 王龙 et al., 2022). Due to climate change, sustainability, and health purposes, it is essential to develop strategies to maximize sesame yield under reduced N application rates. The low branching ability of sesame made the crop suitable for PD. Fortunately, it was found that yield is closely related to capsule numbers in sesame, and capsule numbers per unit area increased significantly with PD (Ramazani, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Another study revealed that increasing PD coupled with reduced N rate significantly improves crop yield and resource utilization (Duan et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). In this study, we identified the optimal PD of 190,000 plants\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and an N application rate of 60 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for maximizing sesame YPUA. Notably, the highest yield was 2690.02 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e under PD of 190,000 plants\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and nitrogen rate of 60 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, which was a 50% reduction in the actual recommended N rate and a 26.82% yield increment compared to the control (null nitrogen). Significant increases in biomass and nitrogen accumulation were also recorded under these optimal rates. The highest NUE of 1.46\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07% was achieved under D19N60. These results show that the optimized PD and N rate can be promoted to improve sesame YPUA and simultaneously minimize environmental pollution risk and potential health concerns due to N loss. The increase in sesame YPUA, coupled with reduced N input, may significantly improve the incomes of smallholder sesame farmers.\u003c/p\u003e\u003cp\u003eExtremely dense planting led to a significant reduction in yield and NUE. These results indicate that increased PD causes competition for nutrients, water, and light among sesame plants. The light deficiency may have caused a significant reduction in photosynthesis efficiency and, ultimately, weak anabolism and decreased yields. A previous study showed that the proportion of stems increased with the increase in PD (Duan et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Postma et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), which was consistent with the results of our experiments. At the same time, the dry matter and N accumulation of stems, leaves, and shells increased with the increase in N application rate, which may be the main reason for the low NUE under high N rate conditions. As support, the N application rate was significantly and negatively correlated with NUE, NUpE, and AEN, while PD was significantly negatively correlated with yield components.\u003c/p\u003e\u003cp\u003ePC, OC, and FA composition are critical quality traits in sesame (Wei et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The OC and PC of sesame seeds are significantly and negatively correlated (Li et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Herein, we also recorded a negative correlation between OC and PC. The PC significantly increased with the increase in N application rate and decreased with the increase in PD. In contrast, the OC significantly dropped with increased N rates, but the reduction was less with increased PD. These results support the statement of enhanced competition for nutrients and light under extremely dense planting. The PD and N rates significantly affected the FA profile of sesame seeds. The reduction in OC, coupled with the alteration of FA composition and the increase in PC, along with the N rate increase, could be explained by enhanced N assimilation processes under high N rate conditions, which led to a reduced allocation of intermediate metabolic resources required for the synthesis of oil body. For instance, in soft wheat, it was found that reduced N rate and PD modify the supply of free amino acid to protein synthesis and the expression of the storage protein gene (B. Zheng et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Also, pyruvate kinase and phosphoenol pyruvate carboxylase play a central role in modulating N assimilation and amino acid biosynthesis, ATP production via oxidative phosphorylation, and plastidial fatty acid synthesis. The proportion of UFA was increased by reducing the N application rate, which is consistent with reports in other plants (Nosheen et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Sharifi, Namvar, \u0026amp; Seyed-Sharifi, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Taken together, the results show that appropriate PD combined with a reduced amount of N supply may minimize environmental pollution risks and ensure improved yield and seed quality in sesame. Similar cultivation indications have been recommended in soft wheat to guarantee high yields and satisfactory grain quality (B. Zheng et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). We have provided regression equations that may facilitate the optimization of PD and N rates according to needs. The optimal PD of 190,000 plants\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and N application rate of 60 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e identified in this study should be further tested in different environments and on different soils for validation before being promoted.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eOverall, the yield and quality characteristics of sesame were analyzed under different N and PD conditions in this study. We found that an optimal PD of 190,000 plants\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e coupled with an N application rate of 60 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e could be applied for improving sesame yield, biomass, NUE, nitrogen allocation to seeds, and seed quality traits, including PC, FA composition, and oil content. Higher N-dose improved seed PC but significantly reduced NUE, OC, and UFA content. Correlations between PD/N rate and NUE, yield and quality traits are revealed. Our results will guide the sustainable and environmentally friendly enhancement of sesame NUE, production, and quality.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was funded by the Key Development Program Project in Jiangxi Province (20243BBH81029), Jiangxi Agriculture Research System (JXARS-18), and the Sesame Seed Joint Research Project of Jiangxi Province.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available from the corresponding author upon reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAffiliation:\u003c/strong\u003e Key Laboratory of Crop Physiology, Ecology, and Genetic Breeding, Ministry of Education/College of Agronomy, Jiangxi Agricultural University, Nanchang 330045, China.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCorrespond\u003c/strong\u003e\u003cstrong\u003eing author\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003eZiming Wu, [email protected].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; contribution:\u003c/strong\u003e M.W., Z.W., and S.F. designed the experiment. M.W. performed the experiments. X.W., G.W., H.Y., T.S., and Z.W. participated in conducting the experiment. X.Y. contributed to the seed quality analyses. M.W. analyzed the data and wrote the draft. Z.W. reviewed the final manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics Declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBasso, B., Cammarano, D., Troccoli, A., Chen, D., \u0026amp; Ritchie, J. T. (2010). Long-term wheat response to nitrogen in a rainfed Mediterranean environment: Field data and simulation analysis. \u003cem\u003eEuropean Journal of Agronomy, 33\u003c/em\u003e(2), 132-138. doi:https://doi.org/10.1016/j.eja.2010.04.004\u003c/li\u003e\n\u003cli\u003eDeme, P., Narasimhulu, C. 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Effects of plant density on cotton yield components and quality. \u003cem\u003eJournal of Integrative Agriculture, 15\u003c/em\u003e(7), 1469-1479. doi:https://doi.org/10.1016/S2095-3119(15)61174-1\u003c/li\u003e\n\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":"planting density, nitrogen application, sesame, yield, NUE","lastPublishedDoi":"10.21203/rs.3.rs-8083903/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8083903/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eMaximizing crop yield per unit area under minimal fertilizer input is crucial with minimal fertilizer input is crucial to achieving sustainable agriculture. Although dense planting has been adopted by some sesame farmers to improve yield, the practice lacks optimization. Hence, this study was conducted to determine an optimal planting density (PD) and nitrogen (N) application rate for enhancing sustainable sesame production and quality. We simultaneously investigated the impacts of PD and N-dose on sesame nitrogen use efficiency (NUE), biomass production, N allocation to organs, and seed yield and quality. Through field experiments under different PDs and N supplies and statistical analyses, we identified 190,000 plants\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (PD) and 60 kg\u0026middot;hm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (N-dose) as optimal conditions for sustainable improvement of sesame production. Notably, sesame yield, NUE, biomass accumulation, and seed quality traits, including protein content, fat content, and fatty acid composition, were maximal under these optimal conditions. The nitrogen allocated to seeds under these optimal conditions was significantly higher than that to stems, leaves, and capsules. Correlation analysis revealed that PD is significantly negatively associated with the number of capsules, seed number per capsule, 1000-seed weight, protein content, and linoleic acid content. N rate exhibited a significant positive correlation with protein content, total biomass, and total N content, as well as a significant negative correlation with NUE. Our findings may guide land-use efficiency for sesame farming systems and contribute to the sustainable production of high-quality sesame.\u003c/p\u003e","manuscriptTitle":"Optimizing planting density and nitrogen input for improved nitrogen use efficiency, yield and seed quality in sesame","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-26 12:12:00","doi":"10.21203/rs.3.rs-8083903/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":"3e64d26e-8d2a-40c2-baf4-f93dbd982518","owner":[],"postedDate":"November 26th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":58392195,"name":"Earth and environmental sciences/Environmental sciences"},{"id":58392196,"name":"Biological sciences/Plant sciences"}],"tags":[],"updatedAt":"2026-02-11T13:57:11+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-26 12:12:00","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8083903","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8083903","identity":"rs-8083903","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}