Optimizing maize straw return enhances wheat yield and nitrogen use efficiency while reducing N2O emissions

Crop straw return can not only affect soil fertility & crop productivity, but also influence nitrogen use efficiency (NUE) and nitrous oxide (N₂O) emissions. However, the optimal straw return methods that ensure high yield and NUE (grain yield/total N uptake, %) with less N2O emissions remain inadequately understood. Here, we conducted a two-year field experiment in the North China Plain to investigate the integrated effects of maize straw return on wheat yield, NUE and N₂O emissions with five treatments: straw removal (CK), straw mulch (SM), straw mixed evenly into the 0–10 cm soil layer (SR10), straw mixed evenly into the 0–20 cm soil layer (SR20), and straw mixed evenly with the 0–10 cm soil and then the mixture incorporated into the 10–20 cm soil layer (TB). Results showed that maize straw return significantly increased wheat yield compared to straw mulch, with the method of TB achieving the highest yield (10.63 Mg ha^-1) and NUE (32.97). TB also improved soil organic carbon (SOC) and total N (TN) at the 10–20 cm soil layer, with TN increased by 24.89 % on average compared with SM, promoting soil N uptake by wheat plant and reducing N₂O emissions. Conversely, straw mulch or mixed into 0–10 cm soil layer triggered cumulative N₂O emissions by 22.33 % and 20.39 % compared to TB, respectively, particularly during the early growing stages, due to enhanced nitrification microbial activity and reduced substrate supply for denitrification. TB reduced yield-scaled N₂O emissions by 27.6–29.4 % compared with straw mulch. Structural equation modeling (SEM) revealed that effects of straw return on soil chemical properties (r = 0.37, P < 0.001) and denitrification microbial activity (r = 0.62, P < 0.001) were key drivers of N₂O emissions. These findings highlight that stratified incorporation of straw–soil mixtures is a promising strategy to balance wheat yield, NUE, and N₂O mitigation in intensive wheat–maize cropping systems in the North China Plain.