Synergistic nitrification-inhibiting effect of elemental sulfur and dicyandiamide in a typical vegetable soil

An incubation experiment was conducted to investigate the effect of three nitrification inhibitors dicyandiamide (DCD), elemental sulfur (S0) and thoisulfate (S2O32-) on nitrification of NH4+-N in a typical vegetable soil. The results showed that within 72 day-incubation period, the soil NH4+-N content at DCD+S0, DCD and DCD+Na2S2O3 treatment was 5.8, 5.1 and 5.9 times of that at N treatment, respectively, and soil NH4+-N content at S0 and Na2S2O3 treatment was 1.8 and 1.4 times of that at N treatment, respectively. Soil NO3--N content was obviously lower in nitrification inhibitor treatments than in those without nitrification inhibitor treatments, implying that DCD, S0 and S2O32- could inhibit nitrification of soil NH4+-N in the vegetable soil. Synergistic effect of DCD+S0 and DCD+S2O32- on nitrification inhibition of soil NH4+-N was observed 16 and 8 days after the incubation experiment, respectively. This could be contributed to the effect of S2O32- and S4O62- originated from S0 oxidation in soil on restraining decomposition of DCD, prolonging the time of DCD for nitrification inhibition. It is suggested that application of S0 combined with DCD could be used as a nitrification inhibitor in vegetable soils to increase fertilization nitrogen efficiency.