[Effects of elemental sulphur and dicyandiamide on mitigating NO3- -N leaching loss from vegetable soil]

In a pot experiment with allium as test plant and NH4HCO3 as nitrogen source, this paper studied the effects of element sulphur (S0) and dicyandiamide (DCD) on mitigating the NO3- -N leaching loss from soil and on soil inorganic nitrogen (NO3- -N and NH4+ -N) content. The results showed that within the 12 weeks of the experiment, the cumulative leaching loss of soil NO3- -N in treatments S0 + DCD and S0 was 83%-86% and 83% lower, while that of soil NH4+ -N was 16.8-21.0 mg x pot(-1) and 20.4-25.0 mg x pot(-1) higher than CK, respectively, and the cumulative loss of soil (NH4+ + NO3-)-N was 60% lower. By the end of the experiment, soil inorganic nitrogen content in treatments S0 + DCD and S0 was 79.9%-85.4% and 74.9-82.6% higher than CK, respectively. The cumulative leaching loss of inorganic N in treatment S0 + DCD was 4.6%-14.4% and 15.4%-30.1% lower, and the soil inorganic nitrogen content by the end of the experiment was 6.1% and 16.8%-36.0% higher than that of treatments S0 and DCD, respectively. Similar results were obtained when S0 was replaced by Na2S2O3, but not by Na2SO4. The fact that the application of S0 could obviously decrease the NO3- -N leaching loss from soil could be contributed to the inhibitory effects of S2O3(2-) and S4O6(2-) originated from S0 oxidation in soil on the nitrification of NH4+ -N. S0 could retard the decomposition of DCD due to the effect of its oxidized products S2O3(2-) and S4O6(2-), and thus, extend the inhibitory effect of DCD on NH4+ -N nitrification. It is suggested that S0 combined with DCD could be used as an effective nitrification inhibitor to control the NO3- -N leaching loss from vegetable soils.