Optimized nitrogen allocation in cotton-soil system improves cotton production and nitrogen utilization efficiency under wheat-cotton straw return in East China

In wheat-cotton rotation system, the strained photo-thermal resources after harvesting wheat pose challenges to cotton growth in terms of the utilization of temperature, light and fertilizer, especially in nitrogen. The purpose of the study was to explore suitable agricultural management practices for sustainable cotton production and soil productivity under wheat-cotton system. Two straw managements (straw return and straw removal) and four nitrogen rates (0, 75, 150 and 300 kg N ha −1 , defined as N0, N75, N150 and N300, respectively) were adopted as the variables. The results showed that under straw return with N150, where cotton yield and fiber quality reached to the maximum, the highest apparent nitrogen recovery efficiency of 75.9 %–92.7 % and the maximum ratios of cotton boll number and cotton yield over the efficient photo-thermal phase to them at the harvesting stage were obtained. 15 N-labeling indicated that optimal nitrogen application could improve fertilizer nitrogen uptake in cotton before flowering and straw return increased cotton nitrogen uptake from soil. Furthermore, straw return increased nitrogen fertilizer retention at the 0–20 cm soil depth. Under straw return with N150, more nitrogen fertilizer was stored as organic nitrogen (40.9 %) and microbial biomass nitrogen (11.8 %). Therefore, increasing nitrogen fertilizer retention in the topsoil might attribute to improving microbial nitrogen fixation. In addition, straw return improved fertilizer nitrogen that cotton boll allocated to fiber and that seedcotton allocated to seed kernel and fiber at N150. According to these findings, we are led to conclude that under straw return, optimal nitrogen application of N150 improved cotton boll development over the efficient photo-thermal phase and nitrogen allocation in cotton-soil system, increasing nitrogen utilization efficiency and cotton production. • Cotton bolls formed over the efficient photo-thermal phase increased ANRE. • Straw return improved nitrogen uptake and retention in the cotton-soil system. • Improving fertilizer nitrogen allocation increased ANRE and cotton production. • Straw return with suitable nitrogen rate is encouraged in double cropping system.