Responses of Soil N2O and CO2 Emissions and Their Global Warming Potentials to Irrigation Water Salinity

Irrigation using marginal quality water (brackish, saline, or treated wastewater, with a salinity of 2–8 g L−1) instead of fresh water alters the soil carbon and nitrogen cycle, and thus, soil greenhouse gas emissions. To reveal the responses of soil nitrous oxide (N2O) and carbon dioxide (CO2) emissions and their global warming potentials (GWPs) to irrigation water salinity, a pot experiment was conducted at three levels (2, 5, and 8 g L−1, namely S2, S5, and S8). The results show that the cumulative soil CO2 emissions were reduced with increases in the irrigation water salinity and were 11.6–28.1% lower than those from the fresh water-irrigated treatment (CK). The cumulative N2O emissions from S2 and S8 decreased by 22.7% and 39.6% (p < 0.05), respectively, in comparison to CK, whereas those from S5 increased by 87.7% (p < 0.05). The cumulative GWPs from S2 and S8 were 19.6% and 44.1% lower than those from CK, while those from S5 were significantly higher (p < 0.05). These findings indicate that reducing the salinity of brackish water from 5 to 2 g L−1 before using it for irrigation is a potential strategy to mitigate soil GHGs and solve water resource scarcity. The response of soil greenhouse gas (GHG) emissions to salinity may be significantly different among irrigation water salinity ranges. The results have an important guiding significance for exploring greenhouse gas emission reduction measures, and sustainable utilization models of water and soil resources.