Optimizing nitrogen fertilizer and straw management promote root extension and nitrogen uptake to improve grain yield and nitrogen use efficiency of winter wheat (Triticum aestivum L.)

Straw returning is an efficient straw usage strategy in rice-wheat rotation, but nitrogen (N) use efficiency (NUE) was decreased due to incorrect straw and N fertilizer managements. To investigate the effects of straw and N fertilizer management on root growth, N fertilizer fates, grain yield and NUE of wheat, a two-year field and micro-plot N-15-labelled experiment under three levels of N application rate (0, 180 and 240 kg N ha(-1)) with two basal N application stages [seeding (BN), and 3-leaf stage (TN)] and three straw treatments [no straw return (NS), straw return by rotary tillage (SR) and straw return by ploughing (SP)] was conducted. The results indicated that SP increased grain yield and NUE, and the increase was highest under TN180. SP increased N uptake by enhancing root extension and soil N supply capacity, and TN decreased N-15 residual in 60-100 cm soil layer. SP and TN180 both decreased N-15 fertilizer loss and increased N-15 recovery. Reducing basal N and applied at third-leaf stage (TN180) under SP had the same grain yield level as conventional N management (BN240) under NS, while highly improved NUE due to more root extension in deep soil layer and less N fertilizer loss.