Effects of Simulated Nitrogen Deposition on Soil Net Nitrogen Mineralization in the Meadow Steppe of Inner Mongolia, China

Effects of simulated nitrogen (N) deposition on soil net nitrogen mineralization (NNM) were examined in situ during two growing seasons, using the resin-core technique in the semiarid meadow steppe in Inner Mongolia, China. The aim of this study is to clarify the effect of N levels (0, 10, and 20 kg N ha −1 yr −1 ) and forms (NH 4 + and NO 3 - ) on soil mineral N and NNM. Our results showed that N levels had no significant differences on soil mineral N and NNM. In the first year, three N treatments ((NH 4 ) 2 SO 4 , NH 4 Cl and KNO 3 ) increased soil NH 4 + concentrations but had no significant effects on soil NO 3 - concentrations. In the second year, (NH 4 ) 2 SO 4 treatment increased soil NO 3 - concentrations, NH 4 Cl and KNO 3 treatments decreased them. Three N treatments significantly decreased soil NH 4 + concentrations in the later stages of the second year. As for the soil NNM, three N treatments had no significant effects on the rates of soil NNM ( R m ) and net nitrification ( R n ) in the first year, but significantly decreased them in the second year. The contribution of N addition to R m was higher from (NH 4 ) 2 SO 4 than from NH 4 Cl and KNO 3 . However, Soil R m was mainly affected by soil water content (SWC), accumulated temperature (T a ), and soil total N (TN). These results suggest that the short-term atmospheric N deposition may inhibit soil NNM in the meadow steppe of Inner Mongolia.