Optimizing N rates enhanced crop yields and mitigated N2O emissions in a peanut–wheat cropping system in the North China Plain

Optimal nitrogen (N) inputs are critical for reconciling crop yields with greenhouse gas (GHG) mitigation in agroecosystems. The peanut-wheat cropping system has been shown to reduce synthetic N inputs through biological N fixation and legacy effects in the North China Plain (NCP). However, excessive N input remains prevalent in this region, and system-level responses to N optimization are not well understood. A three-year field experiment was conducted with five N application rates (0–200 kg N ha−1 for the peanut; uniform 120 kg N ha−1 for the wheat) to evaluate their effects on soil carbon and N dynamics, GHG emissions, and crop productivity. Increasing N inputs enhanced N2O emissions by 211‒481% during the peanut season, likely driven by increased soil mineral N availability. In contrast, this effect was limited in the subsequent wheat season, as uniform N application diminished treatment contrasts and masked residual N effects. Consequently, cumulative N2O emissions increased by 66‒153% across the peanut-wheat system. Higher N rates primarily increased soil mineral N stocks and negatively affected soil organic carbon sequestration. Importantly, moderate N input (150 kg N ha−1) achieved yields comparable to the 200 kg N ha−1 treatment, indicating no yield penalty under optimized N management. Although differences in net global warming potential (net GWP) and net ecosystem economic benefit (NEEB) were not statistically significant, 150 kg N ha−1 showed the best performance, balancing environmental and economic outcomes. These results provide a basis for optimizing N application in similar regions to achieve high yield, reduced emissions, and coordinated development in peanut-wheat systems.