Effects of different nitrification inhibitor combinations on the transformation of ammonium nitrogen in black soil and cinnamon soil

Objectives Adding nitrification inhibitors and nitrogenous fertilizer synergist is an effective way to improve the utilization rate of nitrogenous fertilizer. The effects of different nitrification inhibitors and nitrogenous fertilizer synergist on the transformation of ammonium nitrogen in soil with different properties were studied for the choice of available inhibitors in different soils.

Methods The tested biochemical inhibitors included 2-chloro-6 (trichloromethyl) -pyridine (CP), 3, 4-dimethyl-pyrazole phosphate (DMPP), 1-methoxyl-3-methylpyrazole (CMP), 3-methylpyrazole (MP), 2-amino-4-chloro-6-methylpyrimidine (AM), N-guard, dicyandiamide (DCD). The tested soils were black soil and cinnamon soil, and ammonium chloride was used as nitrogen fertilizer. The stable fertilizer was prepared by adding above mentioned individual or several biochemical inhibitors according to the usual dosage. A indoor culture experiment was conducted at constant temperature. The contents of NH₄⁺-N and NO₃^–-N in soil were measured at 1, 4, 7, 11, 15, 22, 30, 45, 60, 75, 90, 105, 120 days since the beginning of culture experiment, and the inhibition rates of nitrification were calculated.

Results In the black soil and the cinnamon soil, the transformation characteristics of ammonium nitrogen were significantly different, and the nitrification rate in the weakly acidic black soil was significantly lower than that in the alkaline cinnamon soil. In black soil, nitrification inhibitor treatments of N+CP, N+CP+N-guard, N+CP+DMPP, N+CP+DCD, N+CP+CMP, N+CP+AM and N+CP+MP all showed good inhibition effect, which could maintain high NH₄⁺-N content in black soil for more than 120 days. At the 120 days, the nitrification inhibition rates of N+CP, N+CP+DCD and N+CP+N-guard were 37%–40%, while those of N+CP+AM, N+CP+MP, N+CP+DMPP were 32%–36% and that of N+CP+CMP was 26%. In the cinnamon soil, the N+CP+DCD combination had the most effective nitrification inhibition. At 120 days of cultivation, the nitrification inhibition rate was 20%. The nitrification inhibition rates of N+CP and N+CP+AM were 23% and 12% respectively at the 105 days, 63% and 60% respectively at the 90th day. The nitrification inhibition rates of N+CP+N-guard, N+CP+DMPP, N+CP+MP, and N+CP+CMP were 43%, 42%, 37% and 35% respectively at the 75th day of culture, and the effective nitrification inhibition time could last for about 75 days.

Conclusions Specific nitrification inhibitors or combinations should be added to make efficient and stable ammonium nitrogen fertilizer when using ammonium chloride as nitrogen fertilizer in soils with different pH values. The nitrification inhibitor CP alone or CP+N-guard and CP+DCD combination perform significant and long inhibition on the transformation of ammonia nitrogen in acidic black soil. The CP+DCD combination works well on arid and semi-arid alkaline cinnamon soil.