Organic fertilizer substitution delays leaf senescence and improves source–sink balance in winter wheat under different precipitation types

BACKGROUND To elucidate the regulatory effects of organic fertilizer substitution on leaf senescence and source–sink relationships in dryland winter wheat under different precipitation types, a long‐term fertilization experiment was conducted in Heyang County, Shaanxi Province, with three consecutive seasons of field trials analyzed from 2022 to 2025 (based on a trial initiated in 2017). The experiment included two fertilization types: conventional chemical nitrogen fertilizer (CN) and 25% organic nitrogen substitution (MN). Each type comprised four N application rates (60, 120, 180, and 240 kg N ha −1 ), along with a blank control (N0, no nitrogen applied). RESULTS Results demonstrated that precipitation types exerted a stronger regulatory effect than N fertilization. The MN treatment significantly prolonged the grain‐filling period, delaying its cessation by 0.12–1.48 days relative to chlorophyll senescence. While the N180 treatment achieved the optimal source–sink ratio, differences among the N120 and N240 treatments were not significant. Grain yield responses varied with precipitation types: the CN240 treatment maximized grain yield in wet years, while the MN180 and MN120 treatments were optimal in normal and dry years, respectively. CONCLUSION Consequently, 25% organic fertilizer substitution combined with 180 kg N ha −1 may serve as a relatively robust baseline N management strategy for dryland winter wheat under the rainfed agroecological conditions of Heyang County on the Loess Plateau, as it effectively coordinated leaf senescence with grain filling.