Promoting pre-anthesis nitrogen accumulation in wheat to achieve high yield and nitrogen-use efficiency through agronomic measures

Improvements in grain yield and nitrogen (N)-use efficiency (NUE) are being sought to combat the excessive application of N fertilizer in the rice-wheat rotation system in China. Improving N-uptake efficiency (NUpE) is expected to explore the synergy of grain yield and NUE, but the accumulation and remobilization of N in wheat with high NUpE is still obscure. A 2-year field experiment was conducted to study how to improve NUpE through crop management of planting densities, N application splits, and wheat growth stages when the last N was topdressed. In both years, NUpE was significantly positively related to grain yield and NUE. Comparing with the low and medium NUpE groups (grouping the treatments using cluster analysis of NUpE), the high NUpE group had more total N accumulation as a result of absorbing abundant N from re-greening (Zadoks growth stage, GS25) to anthesis (GS60), and higher N accumulation in grains mainly due to increasing N remobilization from the vegetative organs. Our results indicated that improving the planting density (from 150 to 225 plants m−2) promoted N accumulation before stem elongation (GS30). Late application of more N fertilizers (N application splits 3:1:3:3 versus 5:1:2:2) and relatively early application of the last N portion [topdressing when the flag leaf was visible (GS37) or at booting (GS45) versus topdressing at heading (GS55) or anthesis] boosted N accumulation from stem elongation to anthesis. Finally, a combination of agronomic measures was proposed to achieve high yield and NUE through promoting pre-anthesis N accumulation and NUpE.