Vermicompost maintains fertility of topsoil by reducing NH3 volatilization and improving 15N/NO3- retention 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 measured by open static chamber method (sponge sampling) and distribution of 15N and NO3- concentration in layers in a 30-cm soil column experiment with vermicompost addition after incorporation of 15N-labeled urea in upper (0-10 cm) saline-alkali soil. Destructive sampling was conducted at 20 and 60 days of the experiment to investigate influencing factors of NH3 volatilization and 15N/NO3- retention, respectively. Vermicompost was used to reduce NH3 volatilization and improve distribution of 15N/NO3- of saline-alkali soil in this study. The results showed that vermicompost addition decreased total NH3 volatilization by 45.1% compared to the untreated saline-alkali soil, decreased the 15N in the bottom soil layer (20-30 cm) by 17.1% and increased the 15N concentration in the upper soil by 48.7%. Vermicompost regulated the abundance of amoA/C and NxrA genes, which can decrease NH3 volatilization by converting substrate NH4+ to NO3-. In addition, Ca2+ (+6.2%) is 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 decreasing Cl- by 30.4% in the upper soil. The study concluded that vermicompost addition can inhibit N losses by reducing NH3 volatilization and improving 15N/NO3- retention in saline-alkali soil.