Effects of Irrigation Water Salinity on Soil Properties, N2O Emission and Yield of Spring Maize under Mulched Drip Irrigation

Brackish water has been widely used to irrigate crops to compensate for insufficient freshwater water supply for agricultural use. The goal of this research was to determine an efficient brackish water use method to increase irrigation efficiency and reduce N2O emission. To this end, we conducted a field experiment with four salinity levels of irrigation water (1.1, 2.0, 3.5, and 5.0 g·L−1 with drip irrigation) at Hetao Irrigation District (Inner Mongolia, China) in 2017 and 2018. The results show that irrigation with 3.5–5.0 g·L−1 water salinity increased the soil salinity compared with irrigation using 1.1–2.0 g·L−1 water salinity. The soil water content with 5.0 g·L−1 brackish water irrigation was significantly higher than with 1.1–3.5 g·L−1 water salinity due to the effect of salinity on crop water uptake. The overall soil pH increased with the increase in irrigation water salinity. Saturated soil hydraulic conductivity decreased with the increase in irrigation water salinity. These results indicate that brackish water irrigation aggravates the degree of soil salinization and alkalization. The soil N2O cumulative flux resulting from irrigation with 5.0 g·L−1 water salinity was 51.18–82.86% higher than that resulting from 1.1–3.5 g L−1 water salinity in 2017, and was 32.38–44.79% higher than that resulting from 1.1–2.0 g·L−1 in 2018. Irrigation with brackish water reduced maize yield, and the reduction in yield in 2018 was greater than that in 2017, but irrigation with 2.0 g·L−1 brackish water did not significantly reduce maize yield in 2017. These results suggest that reducing the salinity of irrigation water may effectively reduce soil N2O emission, alleviate the degree of soil salinization, and increase crop yield.