Effects of Combined Nitrification Inhibitors on Nitrogen Transformation, Maize Yield and Nitrogen Uptake in Two Different Soils

Nitrification inhibitors (NIs) affect nitrogen (N) cycle and crop yield, but how the combinations of NIs influence N transformation and maize yield remains unclear. An outdoor pot experiment was performed to explore the effect of three NIs (nitrapyrin (CP), 3, 4-dimethylpyrazole phosphate (DMPP) and dicyandiamide (DCD)) and their combinations on mineral N transformation, yield and N use efficiency (NUE) of maize in a brown soil and a cinnamon soil from northeast China. Higher yield and NUE were obtained in the brown soil than that in the cinnamon soil. All treatments with NIs significantly increased NH4+-N content, grain yield and NUE in both soils, especially for NIs combination (DMPP + DCD in the brown soil and CP + DCD in the cinnamon soil). These two treatments significantly increased yield and apparent nitrogen recovery by 1.84 and 2.31 times, 10.24 and 6.39 times, respectively, compared with N fertilizer treatment. They also showed lower apparent nitrification rates (17.2% and 53.7%, respectively) compared with single NIs treatments. Considering both the inorganic N supply and agronomic effect of NIs, DMPP + DCD and CP + DCD are the best strategies for the application of NIs in the brown soil and cinnamon soil.