Effect Of Element Sulphur And Dicyandiamide On Leaching Loss Of NO₃～--N From Vegetable Soil

The leaching loss of NO3- from soils not only decrease fertilization nitrogen efficiency, but also result in pollution of surface/ground water. One incubation and two leaching experiments were conducted to investigate the effect of supplied element sulphur (S0) and DCD on leaching loss of NO3-from vegetable soil, and nitrification of soil NH4+.The results of soil incubation experiment was summarized as bellow:1. Added S0 and DCD could inhibit nitrification of soil NH4+, decrease soil NO3--N content, and maintain a high soil NH4+-N content within 72 days at NH4HCO3 treatment, and within 48days at urea treatment. During period of incubation for 72 days, treatments of DCD+S0, DCD+Na2S2O3 and DCD showed high nitrification ratio among of seven treatments, nitrification ratio followed the decrease order as bellow: DCD+S0 > DCD+Na2S2O3 >DCD.2. Average soil NH4+-N contents was 27.7 - 31.3 mg/kg at DCD treatment, which was 2.6-2.7 times and 3.1 -3.9 times of those at S0 and Na2S2O3 treatment respectively, implying DCD had the best nitrification inhibition among of three inhibitors (DCD, S掳,Na2S2O3). The nitrification inhibition was greater at treatment of DCD combined with S掳or Na2S2O3 than DCD treatment. This could be contributed to inhibition of S2O32- originated from oxidation of S0 on decomposition of DCD.The results of leaching experiment was summed up as fellow:1. Added S0 and DCD could decrease obviously leaching loss of nitrogen, increase inorganic nitrogen content in soil. Inhibition effect of S0 and DCD on leaching loss of nitrogen was in dependence on soil types, which was greater on the Fimic Anthrosols than on the Calcaric Cambisol. On the Calcaric Cambisol, The NO3--N was predominately nitrogen forms in soil and exuates. An obvious inhibition of added S0 and Na2S2O3 on leaching loss of nitrogen from soil was observed, however the effect was not found at DCD treatment. Under the condition of urea and NH4HCO3 as nitrogen source, leaching loss of NO3--N at added S0 treatment decreased by 40.4% and 10% relative to without S掳 treatment,leaching loss of NO3'-N at added NaS2O3 treatment decreased by 59% and 10.5% relative to without S treatment. On the Fimic Anthrols, the NH4+-N was predominately inorganic nitrogen forms in soil. Treatments of S+DCD and S had a lowest leaching loss of NO3'-N among seven treatments, less than 70% cumulative leaching loss of NO3~-N was found at treatments of S+DCD and S relative to CK.2. Effect of nitrification inhibitor on leaching loss of nitrogen was in dependence on soil types, inhibitor, and nitrogen sources. On the Calcaric Cambisol, Na2S2O3 showed the best inhibitor in decreasing leaching loss of nitrogen, followed by S. On the Fimic Athrosols, S was the best inhibitor in decreasing leaching loss of nitrogen, and the next Na2S2O3. Leaching loss of NO3~-N was less at treatment of DCD combined with S掳or Na2S2O3 than DCD treatment. Inhibition effect of S and Na2S2O3 on leaching loss of NO3--N was better at urea treatment than at NH4HCO3 treatment. It could be contributed to inhibition of S2O32- and S4O62- originated from oxidation of S掳 in soil on urease activity.3. Application of S and DCD could increase vegetable yield, and reduce NO3~-N content in tissues of vegetable. Under the condition of urea as nitrogen source, and biomass yield of greengrocery was 24.6% and 15.8% greater at treatments of DCD and S+DCD than CK. Under the condition of NH4HCO3 as nitrogen source, biomass yield of greengrocery was 24.5% and 14.8% greater at S+DCD and S treatment than CK. The NO3-N content in tissues of vegetable were 44.8% ~ 64.5%, 31.7% ~ 50.6% and 34.9% -49.3% lower at treatments of S, DCD and Na2S2O3 relative to CK.To integrate the present study result, we suggested that S and S+DCD could be used as nitrification inhibitor to postpone nitrification of NH4+- N, subsequently decrease leaching loss of NO3--N from vegetable soil with low soil available sulphur.