Timing and splitting of nitrogen fertilizer supply to increase crop yield and efficiency of nitrogen utilization in a wheat–peanut relay intercropping system in China

Agronomically optimizing the timing and rates of nitrogen (N) fertilizer application can increase crop yield and decrease N loss to the environment. Wheat (Triticum aestivum L.)–peanut (Arachis hypogaea L.) relay intercropping systems are a mainstay of economic and food security in China. We performed a field experiment to investigate the effects of N fertilizer on N recovery efficiency, crop yield, and N loss rate in wheat–peanut relay intercropping systems in the Huang-Huai-Hai Plain, China during 2015–2017. The N was applied on the day before sowing, the jointing stage (G30) or the booting stage (G40) of winter wheat, and the anthesis stage (R1) of peanut in the following percentage splits: 50-50-0-0 (N1), 35-35-0-30 (N2), and 35-0-35-30 (N3), using 300 kg N ha−1, with 0 kg N ha−1 (N0) as control. 15N-labeled (20.14 atom %) urea was used to trace the fate of N in microplots. The yields of wheat and peanut increased by 12.4% and 15.4% under the N2 and N3 treatments, relative to those under the N1 treatment. The 15N recovery efficiencies (15NRE) were 64.9% and 58.1% for treatments N2 and N3, significantly greater than that for the N1 treatment (45.3%). The potential N loss rates for the treatments N2 and N3 were 23.7% and 7.0%, significantly lower than that for treatment N1 (30.1%). Withholding N supply until the booting stage (N3) did not reduce the wheat grain yield; however, it increased the N content derived from 15N-labeled urea in peanuts, promoted the distribution of 15N to pods, and ultimately increased pod yields in comparison with those obtained by topdressing N at jointing stage (N2). In comparison with N2, the N uptake and N recovery efficiency (NRE) of N3 was increased by 12.0% and 24.1%, respectively, while the apparent N loss decreased by 16.7%. In conclusion, applying N fertilizer with three splits and delaying topdressing fertilization until G40 of winter wheat increased total grain yields and NRE and reduced N loss. This practice could be an environment-friendly N management strategy for wheat–peanut relay intercropping systems in China.