Effects of salts and moisture content on N2O emission and nitrogen dynamics in Yellow soil and Andosol in model experiments

The effects of salt type and its concentration on nitrification, N minerali zation and N2O emission were examined under two levels of moisture content in Yellow soil and Andosol samples as simulated to agriculture under arid/s emi-arid conditions and under heavy application of fertilizer in a glass-ho use, respectively. The salt mixtures were composed of chlorides (NaCl and N H4Cl) or sulphates [Na2SO4 and (NH4)(2)SO4] and were added at various conce ntrations (0, 0.1, 0.2, 0.4 and 0.6 M as in the soil solution). These salts were added to non-saline Yellow soil at different moisture con tents (45 o r 40 and 65% of maximum water-holding capacity; WHC) and their effects on t he changes in mineral N (NH4+-N and NO3--N) concentration as well as N2O em ission were examined periodically during laboratory incubation. We also mea sured urease activities to know the effect of salts on N mineralization. Fu rthermore, Ca(NO3)(2) solution was added at various concentrations (0, 0.1, 0.3, 0.5 and 0.8 M as in the soil solution) to a non-saline Andosol taken from the subsurface layer in a glass-house and incubated at different moist ure contents (50% and 70% of WHC) to examine their effects on changes in mi neral N. Nitrification was inhibited by high, but remained unaffected by lo w, salt concentrations. These phenomena were shown in both the model experi ments. It was considered that the salinity level for inhibition of nitrific ation was an electric conductivity (1:5) of 1 dS m(-1). This level was inde pendent of the type of salts or soil, and was not affected by soil moisture content. The critical level of salts for urease activities was about 2 dS m(-1). The emission rate of N2O was maximum at the beginning of the incubat ion period and stabilized at a low level after an initial peak. There was n o significant difference in N2O emission among the treatments at different salt concentrations, while higher moisture level enhanced N2O emission rema rkably.