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.