Vermicompost Improves Fertility of Topsoil by Reducing Ammonia Volatilization and Nitrate Leaching in a Saline-Alkali Soil

Nitrogen loss is a major limiting factor affecting agricultural productivity in saline-alkali soil, with NH3 volatilization and N leaching being the main sources of N loss. In this study, the dynamics of NH3 volatilization was determined by sponge aeration and distribution of NO3- and 15N in different layers in a 30-cm soil column experiment with vermicompost addition after application of 15N-labeled urea in saline-alkali soil. Vermicompost was used as a modifier to study the NH3 volatilization dynamics, NO3- and 15N distribution in this soil. The results showed that vermicompost addition decreased total NH3 volatilization by 45.1%, decreased the leaching of 15N from bottom soil layer (20-30 cm) by 17.1% and increased the 15N concentration in the upper (0-10 cm) soil by 48.7%. Vermicompost regulated the abundance of amoA/C and NxrA genes, which can decrease NH3 volatilization by reducing the volatile substrate NH4+. In addition, Ca2+ (+6.2%) and Mg2+ (+13.5%) were adsorbed by increasing soil cation exchange capacity (+20.6%), thus replacing the adsorption of Na+ (-13.8%) and decreasing the desorption of NH4+. Vermicompost enhanced the adsorption of NO3- by increasing Ca2+ and Mg2+, and the number anion-binding sites retaining NO3- by loss of Cl- (-30.4%) in upper soil, thereby inhibiting NO3- leaching. The study concluded that vermicompost addition can inhibit N losses by reducing NH3 volatilization and nitrate leaching in saline-alkali soil