Mitigating greenhouse gas emissions and ammonia volatilization from cotton fields by integrating cover crops with reduced use of nitrogen fertilizer

Winter cover crop cultivation during the fallow season has been strongly recommended in single crop cropping systems to improve soil quality, but its impact on the soil greenhouse gas (GHG) emissions of the soil has not been extensively studied. This study aimed to investigate the effects of replacing traditional winter fallow with a cover crop combined with a reduced amount of nitrogen (N) fertilizer on ammonia (NH3) volatilization, GHG emissions, and cotton production yield. A field experiment was performed with two cropping systems (a single cotton system and February orchid (Orychophragmus violaceus L.) incorporated into a single cotton cropping system) and four N levels (0, 112.5, 168.75 and 225.0 kg N ha(-1)). The results showed that the incorporation of February orchid increased cotton yield, nitrous oxide (N2O) emission, NH3 volatilization, global warming po-tential (GWP), and net ecosystem carbon budget (NECB) under the same N application rate. Moreover, the NH3, N2O, GWP, yield GWP, and NECB increased with an increasing N application rate. Furthermore, the correlation and redundancy analysis (RDA) results indicated that N2O emissions and NH3 volatilization were positively affected by soil NO3--N, total nitrogen (TN) and lint cotton yield. Overall, compared with the single cropping of cotton with conventional fertilization, the incorporation of February orchid with a 25% reduction in the N application rate decreased NH3 volatilization by 1.05 kg NH3-N ha(-1) and N2O losses by 0.34 kg N2O-N ha(-1) and resulted in a favorable cotton yield. Our results demonstrate that replacing traditional winter fallow with a cover crop combined with a N fertilizer reduction may help to mitigate soil GHG emissions and NH3 volatilization while ensuring yield in cotton production. In future studies, the evaluation of cropping system GHG emissions should be considered from a life-cycle perspective, and attention should be given to the legacy impacts of N.