Integrated crop-N system management to establish high wheat yield population

It is essential to identify the main components that limit crop yield to achieve high crop yields. We collected data from 156 experimental field plots over six crop seasons to determine the degree to which wheat yield is limited by spike number and to further understand the effects of different sowing dates, seeding rates, and nitrogen (N) management on population development and yield. High yields in plots (>8.5 t ha−1) were attributable to increased spike numbers associated with elevated pre-winter stem numbers and higher percentage of productive stems. An early sowing date with a seeding rate of 350 seeds m−2 significantly produced higher spike numbers than a late sowing date with a seeding rate of 540 seeds m−2. High basal N fertilizer rate and dressing N at the regreening stage, typical of farmers' N practices, markedly decreased productive stem percentage compared to an optimal basal N rate and N dressing at the stem-elongation stage. A dressing N rate of 120 kg N ha−1 at stem-elongation stage increased spike number compared to applications of 0 or 60 kg N ha−1. Based on our results, we designed an integrated crop-N management (ICM-N) for generating high yields and high N use efficiency. The ICM-N strategy increased grain yield by 33% (p < 0.05) while using a 27% lower N fertilizer rate led to an 87% increase in N use efficiency over three crop seasons compared to a standard farmers' management strategy.