Assessment of nitrogen fertilization in cotton/soybean intercropping using the 15N isotope dilution method

Abstract

AbstractIntercropping of cotton and legume plants offers long‐term crop productivity while saving agricultural resources and improving soil health. However, the use of nitrogen (N) in cotton/legume intercropping systems requires further evaluation. In this study, three N fertilization rates (cotton/soybean: 160/20, 320/40 and 480/80 kg N ha−1) incorporating three root barrier systems (complete, semi and no root barrier between the crops) under cotton/soybean intercropping systems were conducted to assess interactions between N supply and N transfer, recovery and residue using the 15N isotope dilution method. The results show that cotton was a stronger competitor for N than soybean plants. The 320/40 kg N ha−1 treatment with no root barrier system inhibited the growth of soybean, while the growth, productivity and N uptake for cotton were maximized. The N fixation rate (%NDFA) in soybean and N transfer rate (%NTFS) from soybean to cotton decreased with the increasing N fertilizer application rate, whereas the intercropping system with no root barrier increased %NDFA and %NTFS. The higher N fertilization rate increased the N residue on the side of cotton, whereas the intercropping with no root barrier increased N utilization rate (%NUR) and reduced N residue rate (%NRR). The N transfer amount (NTA) was positively correlated with cotton yield, dry matter (DM) and N uptake, while NTA was negatively correlated with these indicators for soybean. Overall, cotton/soybean intercropping adapted to the 320/40 kg N ha−1 condition and intercropping with no root barrier system by balancing growth, changing N uptake and regulating N fixation transfer, mitigating the issue of N residue.