Efficacy of four nitrification inhibitors for the mitigation of nitrous oxide emissions under different soil temperature and moisture

Background Nitrification inhibitors (NI) may be used to inhibit nitrous oxide (N2O) emissions from agricultural soils, but their efficacy could be strongly affected by soil temperature and moisture. Aims This study investigated how different NI behave in a sandy soil under variable temperature and moisture levels, which currently remains unclear. Methods Efficacies of four NI [dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP), nitrogenous mineral fertilizers containing the DMPP ammonium stabilizer (ENTEC) and active ingredients: 3.00%-3.25% 1,2,4-triazole and 1.50%-1.65% 3-methylpyrazole (PIADIN)] were investigated in an incubation experiment under two soil temperatures (15 and 25 degrees C) and two moisture levels [60% and 80% water-holding capacity (WH)] for 60 days in a sandy soil. The soil received 0.5 g NH4+-N kg(-1) soil and the inhibitors were applied at 5% of applied N. Total N2O emissions were calculated based on gas samples collected throughout the incubation period. Results Increasing soil temperature from 15 to 25 degrees C decreased N2O emissions by 73%-191% while increasing soil moisture from 60% to 80% WHC caused a 109%-251% increase in the emissions. ENTEC followed by DCD were the least effective inhibitors to reduce N2O emissions under all temperature and moisture combinations. Depending upon temperature and soil moisture, DMPP and PIADIN inhibited 85%-100% of N2O emissions. At 15 degrees C, both DMPP and PIADIN almost completely inhibited N2O emissions. At 25 degrees C, the efficacy of PIADIN decreased to 88%, while that of DMPP ranged from 86% to 98%. Increased soil moisture content improved the efficacy of all the NI. Conclusions Overall, DMPP and PIADIN were more effective than DCD in a sandy soil under both the soil moisture levels and temperatures. DMPP was the most effective inhibitor, completely inhibiting N2O emissions at 15-25 degrees C and up to 80% WHC in this soil, and is therefore recommended for use in agricultural lands. The concentration of the NI contained in ENTEC was insufficient to affect nitrification at the both soil moisture levels and temperatures.