Molecular Soil Biology 2025, Vol.16, No.6, 325-334 http://bioscipublisher.com/index.php/msb 326 formation of branches and pods, as well as the seed filling capacity. The biological yield of winter rapeseed is the product of growth rate and the length of the growing season, while an increase in the harvest index can significantly increase seed yield. In yield composition, the number of pods per plant is usually considered a key trait determining yield, its essence depending on the survival rate of branches, flowers, and young pods, rather than the potential number of flowers or pods. Appropriate nitrogen fertilizer levels and management can significantly increase the number of pods per plant, the number of branches, and the number of seeds per pod. Rapeseed yield is highly sensitive to seasonal conditions, with differences in planting time, precipitation, and temperature patterns in different years leading to yield variations of approximately 80%. Under drought and water deficit conditions, rapeseed maintains leaf function and tries to maintain the supply of photosynthetic products by regulating osmotic adjustment substances (soluble sugars, proline) and antioxidant enzyme activity, but yield and pod number still decrease significantly. 2.2 Water requirements at different growth stages The water requirements of rapeseed throughout its entire growth period are significantly stage-dependent. The seedling and overwintering stages require moderate water to ensure seedling emergence and safe overwintering, while the branching-flowering-pod filling stage is the peak period of water demand. Water availability is the dominant factor for winter rapeseed seed yield and oil content, especially precipitation and soil moisture conditions during the budding, flowering, and pod filling stages, which have a high explanatory power for yield and oil content variations. In supplementary irrigation experiments in semi-arid regions, supplementary irrigation at the initial flowering stage, when approximately 50% of the effective soil moisture in the root zone is consumed, can maximize yield and economic benefits without significantly reducing water use efficiency; while moderately reducing or stopping irrigation in the later stages of pod filling has limited impact on yield but is beneficial for saving irrigation water. In rain-fed areas with alternating seasonal droughts and floods, cultivation practices such as ridge-and-furrow rainwater harvesting and straw mulching can significantly improve soil water storage and buffer water fluctuations, thereby increasing dry matter accumulation and grain yield (Teymoori et al., 2020). 2.3 Nutrient demand patterns and fertilization response characteristics The optimal nitrogen fertilizer application rate is approximately 120~200 kg N ha-1, which ensures high yield while balancing nitrogen use efficiency and economic benefits. Exceeding this range significantly reduces nitrogen use efficiency and nitrogen partial factor productivity (Zhu et al., 2023). Combined application of nitrogen and phosphorus can increase chlorophyll content, PSII quantum efficiency, and leaf area, extending the grain filling period, while increasing nitrogen alone at high levels does not significantly increase most traits. The yield response of rapeseed to N, P, S, and K follows the order N > P > S > K, and combined application of organic fertilizers (such as farmyard manure and vermicompost) with chemical fertilizers can significantly improve the agronomic efficiency and apparent nutrient recovery rate of major nutrients (Jehangir et al., 2024). In water-deficient or fluctuating water environments, integrated fertilization (chemical fertilizers + organic fertilizers + plant growth-promoting rhizobacteria (PGPR)) can significantly mitigate the adverse effects of drought on grain yield, oil content, and fatty acid composition by increasing antioxidant enzyme activity, maintaining leaf water content, and stomatal conductance. Synergistic application of N and K is crucial for achieving high yield and high nitrogen use efficiency; potassium deficiency will significantly reduce branching and pod number, and increase soil nitrogen surplus; while nitrogen application under sufficient potassium supply can increase nitrogen absorption, nitrogen use efficiency, and reduce nitrogen surplus. 3 Effects of Irrigation Regimes on Rapeseed Yield 3.1 Full irrigation and yield stability In the Trakya region of Turkey, the "full irrigation" treatment, which avoided water stress during flowering, yield formation, and maturation stages, resulted in a seasonal irrigation amount of 251 mm and a total seasonal evapotranspiration of 715 mm, corresponding to a seed yield of 4.80 t/ha, the highest among all treatments (Istanbulluoğlu et al., 2010). Based on a 3-year supplemental irrigation experiment under semi-arid winter rapeseed conditions, all supplemental irrigation treatments significantly increased yield compared to the rain-fed treatment. The "full irrigation" treatment, which replenished soil moisture during three growth stages (vegetative
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