Abstract: By using ¹⁵N pool dilution technique in combining with in situ soil cultivation, this paper studied the effects of nitrification inhibitors dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP) on the gross nitrogen (N) mineralization and nitrification rates in a saline-alkali cinnamon soil in North China. The experiment was carried out in a maize-wheat rotation field in Yuncheng City of Shanxi Province, and three treatments were installed, i.e., urea, urea + DCD, and urea + DMPP. In the first two weeks after fertilization, DCD and DMPP made the gross N mineralization rate and gross N nitrification rate decreased by 25.5% and 7.3%, and by 60.3% and 59.1%, respectively, with a significant difference in the gross N mineralization rate but less difference in the gross N nitrification rate between the effects of DCD and DMPP. However, significant difference was observed in the gross N nitrification rate between the effects of DCD and DMPP after seven weeks of fertilization. The gross N mineralization and nitrification rates and the NH₄⁺ and NO₃^- consumption rates after two weeks of fertilization were 7.2-10.0, 5.5-21.5, 9.1-12.2, and 5.1-8.4 times of those before fertilization, respectively, possibly due to the stimulating effect of N fertilization. DCD and DMPP made the fertilizer urea N more maintained in NH₄⁺-N form and less accumulated in NO₃^--N form in soil. The decreases of the gross N mineralization and nitrifications rate in the test soil due to the effects of the inhibitors would benefit the reduction of N₂O emission from the soil.

Key words: cinnamon soil, nitrification inhibitor, ¹⁵N pool dilution technique, in situ culture, gross N mineralization rate, gross N nitrification rate