Enhanced NO Production Induced by Soil Salinity at a Specific Range.

Nitrous oxide (NO) 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 NO 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. With ammonium-rich organic fertilizer as their N source, the soils were incubated at three soil moisture ( θ ) levels-50%, 75% and 100% of field capacity ( θ fc )-for six weeks. Both NO fluxes and concentrations of ammonium, nitrite and nitrate (NH-N, NO-N and NO-N) were measured throughout the incubation period. The rates of NH-N consumption and NO-N accumulation increased with increasing soil moisture and decreased with increasing soil salinity, while the accumulation of NO-N increased first then decreased with increasing soil salinity. NO emissions were significantly promoted by greater soil moisture. As soil salinity increased from 0.25 to 6.17 dS m, NO emissions from soil first increased then decreased at all three soil moisture levels, with NO emissions peaking at electric conductivity (EC) values of 1.01 and 2.02 dS m. NO emissions form saline soil were found significantly positively correlated to soil NO-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 NO-N accumulation and enhanced NO emissions in soil with a specific salinity range.