Abstract: 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·pot^-1 and 20.4～25.0 mg·pot^-1 higher than CK,respectively,and the cumulative loss of soil (NH₄⁺+NO^3-) 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 Na₂SO 4.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 S₂O₄^2- 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 S₂O₄^2- 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.

Key words: Element sulphur, Vegetable soil, Nitrate, Nitrification inhibitor