Controlled‐Release Urea Combined With Urea Sustains Yield and Improves Soil Organic Carbon Storage Under Reduced Nitrogen in Rice–Wheat Rotation

ABSTRACT Reducing nitrogen (N) input while sustaining productivity is central to the long‐term food security of intensive rice–wheat systems. We evaluated whether blending controlled‐release urea (CRU) with conventional urea (U) could maintain annual yield stability while improving soil carbon status during a 3‐year rice–wheat rotation. Nine treatments, including various combinations of CRU and U as basal and panicle fertilizers, were evaluated. Under both conventional N and reduced N levels, CRU + U outperformed urea alone (CK), with annual yields 15.37% and 8.32% greater, respectively. The 70% CRU + 30% U basal fertilizer treatment increased the plant C content and soil organic carbon (SOC) storage, particularly under nitrogen reduction. CRU application significantly increased the labile organic C fractions (ROC, DOC, and MBC) under reduced N level, increasing SOC lability and the carbon pool management index (CMI). Positive correlations were found among crop yields, the SOC content, and labile organic C fractions, suggesting that improved soil C status is associated with higher crop yields. Furthermore, the straw C input was positively correlated with the CMI, suggesting that carbon accumulation in plant stems and leaves can increase the soil carbon pool and improve subsequent crop yields. Further analysis revealed that as the soil available alkaline hydrolyzable nitrogen (AN) content increased, the SOC content initially increased but then decreased, peaking at 150 mg kg −1 AN. These findings identify a practical N‐management strategy (70% CRU + 30% U basal fertilization mode) for sustaining rice–wheat production with lower N input, with potential benefits for resource‐efficient and climate‐resilient food production.