Effects of combined nitrogen and manure management on yield and nitrate dynamics in winter wheat-summer fallow rotation system

Nitrogen (N) leaching as the major N loss pathway in intensive agricultural systems. However, a comprehensive evaluation for the effects of organic fertilizer substitution on nitrate residue and leaching losses during the fallow season is not available in winter wheat-summer fallow rotation system. The present dryland wheat fertilization experiment conducted from 2014-2019 adopted a split-plot design, with manure dosage (i.e., M-0; NPK group and M-1; MNPK group) as the main plots and nitrogen fertilizer dosage as the subplot (i.e., N-0, N-75, N-150, N-225, N-300). In short, the peaks of NO3- in the 0-200 cm profile gradually move toward the deep soil layer with increasing years of fertilization, and the number of peaks also gradually increases. Increasing the N rate always leads to a sharp increase in nitrate residue in the 0-200 cm profile at the harvest stage (HNR) and sowing stage (SNR) and results in a large amount of nitrate leaching loss (Delta NR) during the summer fallow season, especially when the N rate was> 150 kg ha(-1). Compared to NPK, MNPK significantly increased SNR and Delta NR by 38.1 % and 171 %, respectively, but decreased HNR by 36.2 %. Delta NR was positively related to fallow season precipitation and soil water storage changes during the fallow season in the 0-200 cm profile. When the N rate was> 150 kg ha(-1), the growth rate of grain yield slowed down or even decreased, and the annual average yields of N-75, N-150, N-225, and N-300 were 36.3 %, 51.5 %, 55.4 %, and 47.6 % higher than that of N-0, respectively. The average grain yield of MNPK was 13.9 % higher than that of NPK. Therefore, manure combined with 150 kg ha(-1) N fertilizer is the best fertilization strategy to ensure high productivity of dryland wheat, control nitrate residue, and reduce nitrate leaching loss during the summer fallow season. This results provided valuable information for the application prospect of N fertilizer reduction combined with manure in dryland agriculture.