Negative Pressure Irrigation System Reduces Soil Nitrogen Loss for Lettuce during Greenhouse Production

Negative pressure irrigation (NPI) to grow crops reduces the application of fertilizer and water while also promoting yield and quality. However, plantation vegetables usually require a large input of nitrogen (N) fertilizer in a greenhouse setting, which will lower the soil quality and accelerate the emission of greenhouse gases. Therefore, the purpose of this research was to explore planting lettuce under an NPI system that retrenches N fertilizer application and mitigates N2O emissions compared with conventional irrigation (CI). This research proved that under NPI conditions, nitrate and ammonium fluctuated slightly in the soil, stabilizing in the range of 18-28 mg kg(-1), while that of CI was 20-55 mg kg(-1). The NPI alleviated N2O emissions, and NPI-N150 and NPI-N105 decreased them by 18% and 32%, respectively, compared with those for CI-N150. The main explanation was that the NPI inhibited the formation of NO3--N, reduced the copies number of AOA and AOB as well as the abundance of Nitrospira in the soil, and weakened the soil nitrate reductase and urease activities. The results of this research provide a reliable scientific method for reducing the use of water and N fertilizer while cultivating lettuce, as well as for reducing N2O emissions from agricultural facilities.