Interactive effects of soil amendments (biochar and gypsum) and salinity on ammonia volatilization in coastal saline soil

Ammonia (NH3) volatilization is a major route of nitrogen (N) loss from soil, especially in saline soil. Biochar and gypsum are two important soil amendments that are widely used in coastal saline farmland. However, little is known about the interactive effects of soil amendments and salinity on NH3 volatilization. In this study, five soil salinity levels, three N sources (urea, monoammonium phosphate (MAP), and manure) and two soil amendments (biochar and gypsum, both applied at two rates) were selected to conduct incubation experiments. Nitrogen transformation experiments were conducted simultaneously with NH3 volatilization experiments. The results showed that cumulative NH3 volatilization increased with salinity due to the accumulation of ammonium, which resulted from the inhibition of nitrification by salinity, and also the effect of salinity on soil properties related to NH3 volatilization. Among the tested N sources, the highest NH3 volatilization was observed for urea, followed by MAP and manure, in soils with three different salinity levels. Biochar application increased NH3 volatilization in saline soil, as salt ions constrained the NH3/NH(4)(+ )adsorption capacity of biochar, and the inhibition of nitrification by biochar was aggravated in saline soil. Overall, NH3 volatilization increased with the biochar application rate in saline soil, whereas the effect of a low rate of biochar application on NH3 volatilization was not significant. Gypsum decreased NH 3 volatilization in saline soil, whereas the contribution of different gypsum rates to NH3 volatilization showed no difference. The conclusion could be drawn from the above results that low rates of biochar and gypsum may prevent or reduce NH3 volatilization and nitrogen losses in coastal saline soil.