Excessive N applications reduces yield and biological N fixation of summer-peanut in the North China Plain

Context: The North China Plain (NCP) is China's largest peanut producing area, where winter-wheat summer peanut is an important double cropping system. Excessive nitrogen (N) applications are widely used leading to declined N use efficiency (NUE) and biological N fixation (BNF). However, the influence of excessive fertilizer N inputs on yield and BNF of summer-peanut remains uncertain.Objective: The study aims to evaluate the impacts of different fertilizer N inputs on yield and BNF of summer peanut in the NCP, and explore the optimal N rates for achieving high NUE and low N losses without sacrificing yield. Methods: A three-year field experiment and pot experiment involving five N treatments (N rates with 0, 50, 100, 150, and 200 kg N ha-1, defined as N0, N50, N100, N150 and N200 in the study, respectively) were conducted in the NCP. The jointing use of field experiment and pot experiment were adopted to measure BNF of summer peanut, and the partial least squares path model and a nightingale rose diagram were both included in the study.Results: Summer-peanut yield increased quadratically with increasing N application, but N rates larger than 150 kg N ha-1 caused inadequate seed filling and thus led to slightly reduced yield. Generally, increased N applications significantly increased soil mineral N (SMN) between 0 and 60 cm depth, and dramatically reduced BNF as high SMN strongly inhibits biological nitrogenase activity.Conclusions: The N application required to obtain an optimum yield of 3915 kg ha-1 with relatively high NUEoi (the ratio of N output and N input, 73.0%) and low N losses in the summer-peanut production was 150 kg N ha-1 in the NCP.Implications: The sustainable development of summer-peanut systems will involve reduced N application rates, and N optimization in the winter-wheat summer-peanut rotation should receive further attention considering the N legacy effects.

Automated summary

This study evaluated the effects of different fertilizer nitrogen inputs on the yield and biological nitrogen fixation (BNF) of summer peanut in the North China Plain (NCP). The results showed that the optimal nitrogen application rate for achieving high nitrogen use efficiency (NUE) and low nitrogen losses without sacrificing yield was 150 kg N ha-1, which resulted in a yield of 3915 kg ha-1 and NUEoi of 73.0% in the summer-peanut production. These findings have important implications for the sustainable development of summer-peanut systems.