Enhanced N2O Production Induced by Soil Salinity at a Specific Range

Nitrous oxide (N2O) as a by-product of soil nitrogen (N) cylces, its production may be affected by soil salinity which have been proved to have significant negative effect on soil N transformation processes. The response of N2O production across a range of different soil salinities is poorly documented; accordingly, we conducted a laboratory incubation experiment using an array of soils bearing six different salinity levels ranging from 0.25 to 6.17 dS m(-1). With ammonium-rich organic fertilizer as their N source, the soils were incubated at three soil moisture (theta) levels-50%, 75% and 100% of field capacity (theta fc)-for six weeks. Both N2O fluxes and concentrations of ammonium, nitrite and nitrate (NH4+-N, NO2--N and NO3--N) were measured throughout the incubation period. The rates of NH4+-N consumption and NO3--N accumulation increased with increasing soil moisture and decreased with increasing soil salinity, while the accumulation of NO2--N increased first then decreased with increasing soil salinity. N2O emissions were significantly promoted by greater soil moisture. As soil salinity increased from 0.25 to 6.17 dS m(-1), N2O emissions from soil first increased then decreased at all three soil moisture levels, with N2O emissions peaking at electric conductivity (EC) values of 1.01 and 2.02 dS m(-1). N2O emissions form saline soil were found significantly positively correlated to soil NO2--N accumulation. The present results suggest that greater soil salinity inhibits both steps of nitrification, but that its inhibition of nitrite oxidation is stronger than that on ammonia oxidation, which leads to higher NO2--N accumulation and enhanced N2O emissions in soil with a specific salinity range.