Effect of a Ridge-Furrow Mulching System and Limited Supplementary Irrigation on N 2 O Emission Characteristics and Grain Yield of Winter Wheat ( Triticum aestivum L.) Fields under Dryland Conditions

Knowledge of the characteristics of N 2 O emissions and the influential mechanism is of great significance to mitigate greenhouse gas emissions in semi-arid areas. In the present study, a three-year water-control study was conducted; three simulated rainfall amounts (heavy, normal, and light rainfall = 275, 200, and 125 mm, respectively), two wheat ( Triticum aestivum L. ) planting modes (RF (ridge–furrow mulching system) and TF (traditional flat planting)) and four supplementary irrigation amounts (150, 75, 37.5, and 0 mm) were set up. The effects of different cultivation methods and irrigation amounts on soil N 2 O emissions, the soil water content, available nitrogen content, and denitrifying enzyme activity were investigated to clarify the N 2 O emission mechanism in winter wheat fields ( Triticum aestivum L. ). The results obtained after three years showed that compared with TF, the N 2 O emissions under RF decreased by 21.62–30.72% ( p < 0.001), whereas the soil water content increased by 6.26–8.82%, the available nitrogen content decreased by 1.71–16.24%, and the denitrifying enzyme activities increased by 0.2–24.16% under heavy rainfall conditions. Under conditions with normal and light rainfall, the N 2 O emission fluxes under RF increased by 3.66–12.46% and 6.08–15.57% ( p > 0.05), while the soil water contents increased by 6.13–11.49% and 8.05–13.88%, the soil available nitrogen contents decreased by 11.0–21.42% and 19.93–34.44%, and the denitrifying enzyme activities increased by 0.01–24.08% and 0.03–20.79% compared with TF. Principal component analysis showed that the main factors related to N 2 O emissions under RF were the soil moisture content and available nitrogen content; these factors combined explained 94.37% the variation of the N 2 O emissions. However, the main factors under TF were the soil moisture content and denitrifying enzyme activity; these factors combined explained 85.81%. In the heavy and normal rainfall years, compared with TF, using RF and 75 mm irrigation achieved the goal of reducing water usage as well as decreasing the N 2 O emissions (or N 2 O increase was not significant). In light rainfall years, RF with 150 mm irrigation obtained significant reductions in water usage compared with TF but it also increased the N 2 O emission flux. Under different rainfall years, the yield of RF increased by 2.89–50.44% compared with the TF system, and the increase in wheat grain yield increased with decreasing rainfall.