Nitrogen supply modulates nitrogen remobilization and nitrogen use of wheat under supplemental irrigation in the North China Plain.

Excessive nitrogen (N) input and irrigation exacerbate N leaching in winter wheat production in the North China Plain (NCP). To explore the optimal N for better N remobilization and higher N utilization of wheat under water-saving irrigation will be conductive to less environmental contamination. A field experiment was conducted at 300 (N), 240 (N), 180 (N), and 0 (N) kg N ha of N application under supplemental irrigation (SI) that brought the relative soil water content (RSWC) to 70% at jointing and 65% at anthesis. Compared with N, N improved the free amino acid content in the flag leaf and grain after anthesis, dry matter and plant N accumulation at maturity, N translocation amount of vegetable organs and its contribution to grain from anthesis to maturity. Compared to N and N, N increased the N translocation efficiency of vegetable organs, and reduced the soil NO-N residue in the 60-180 cm soil layer, which contributing to no significant reduction in grain yield and grain protein yield, but higher grain N recovery efficiency (RE), N recovery efficiency (RE), and N partial factor productivity (PFP). Positive relationships were found between leaf N translocation efficiency and grain yield, grain protein yield, PFP, RE, and RE. Therefore, N is appropriate to obtain a steady grain yield over 7.5 t ha for at least 2 years under SI based on RSWC in the NCP.