Molecular Soil Biology 2025, Vol.16, No.6, 325-334 http://bioscipublisher.com/index.php/msb 329 application, the grain yield of the control varieties Huayouza 9 and Zhongshuang 11 increased by 153.2–397.5% and 150.4%~322.9%, respectively, under the optimal combination of N180K120, which was significantly higher than that under single application of N or K (Gu et al., 2024). Potassium deficiency significantly reduces branching and pod number, and decreases nitrogen uptake, leading to a significant increase in soil nitrogen surplus under high nitrogen application conditions; while sufficient potassium application under N 180~270 kg/ha conditions can improve nitrogen recovery efficiency and reduce nitrogen surplus (Li et al., 2023). A phosphorus fertilizer gradient experiment (0~180 kg P ha-1) showed that the seed yield of direct-seeded winter rapeseed increased significantly with P application from 0 to 90 kg/ha, but the yield increase was not significant at 135 and 180 kg P ha-1; P efficiency initially increased and then decreased between 0–90 kg ha⁻ ¹, and decreased significantly after approximately 120 kg P ha-1, with extra P being allocated more to stems and pods, contributing little to seed yield. Based on this, the optimal P application rate for direct seeding is recommended to be 90~120 kg/ha (Wang et al., 2023). 4.3 Fertilization timing and nutrient absorption and utilization efficiency Under three sowing dates and five spring nitrogen management strategies, without nitrogen application, the ratio of total crop nitrogen uptake at harvest to the sum of soil mineral nitrogen and plant nitrogen after overwintering (SNUpE) was 1.13~1.14 (early sowing) and 1.68 (late sowing), reflecting that soil mineralization during the growing season provided an additional 11~38.6 kg N ha-1 of available N; the economically optimal nitrogen application rate (Nopt) under different sowing dates was 148~175 kg N ha-1, corresponding to an apparent fertilizer nitrogen absorption efficiency (FNUpE) of 0.486~0.574, indicating that adjusting spring nitrogen application based on overwintering plant nitrogen content, sowing date, and expected mineralization can reduce total nitrogen application while maintaining a seed yield of 4.34~4.93 t/ha (Rahimitanha et al., 2022). In the rice-rapeseed-rice rotation system in Southwest China, a pot experiment was conducted to adjust the nitrogen application rate during the rapeseed season and the split application pattern during the rice season (40% basal fertilizer + 40% tillering fertilizer + 20% panicle fertilizer). Compared with conventional nitrogen application in the rapeseed season (Nc) + M3 split application pattern in the rice season (PrNcM3), reducing nitrogen in the rapeseed season (Nr) and using the M3 pattern in the rice season (PrNrM3) increased the agronomic nitrogen efficiency and nitrogen partial productivity of rice by 23.9% and 1.6%, respectively, while the total annual system yield only decreased by 3.95% (Ma et al., 2021). For direct-seeded rapeseed, introducing a mixture of controlled-release nitrogen and quick-release nitrogen also showed a significant temporal effect: reducing nitrogen by 25% from the conventional application rate of 180 kg N ha-1 to 135 kg N ha-1, and combining it with 30%~50% controlled-release nitrogen (N135R1–R3), resulted in no significant difference in pod number, seeds per pod, and grain yield compared to the full quick-release nitrogen control. The N135R2 treatment even increased yield by 1.3%, while apparent N recovery rate, agronomic utilization efficiency, and nitrogen partial productivity all showed an initial increase followed by a decrease, reaching their highest values at a 50% controlled-release nitrogen ratio (Hu et al., 2023) (Figure 1). 4.4 Environmental risks of excessive fertilization In conventional high-input systems, rapeseed NUE (crop nitrogen uptake/nitrogen input) often does not exceed 60%, and a large amount of unabsorbed nitrogen is lost through nitrate leaching or in the form of N2O andNH3, putting pressure on water bodies and the atmospheric environment (Bouchet et al., 2016). When the nitrogen application level exceeds the "economically optimal N rate" for the variety and environment, the increase in grain yield tends to flatten or even stagnate, but the oil content decreases, and the grain protein content increases, accompanied by an increased risk of plant lodging and aggravated disease occurrence, thereby indirectly increasing pesticide input and energy consumption (Yahbi et al., 2022). In nitrogen-sulfur fertilization trials in Poland, when N ≥ 180 kg/ha, the energy consumption per unit area increased from 14.5~19.3 GJ/ha to 22.4~27.0 GJ/ha, while the yield increase was limited (Groth et al., 2020).
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