Suitable combination of nitrogen-inhibitors and nitrogen synergist for production of stable ammonium chloride applied to black soil

Objectives The effects of nitrogen-inhibitors were compared in this paper to screen efficient synergists for ammonium chloride fertilizer in black soil.

Methods Nitrification inhibitors 3,4-dimethyl-pyrazolate phosphate (DMPP), dicyandiamide (DCD), 2-chloro-6-trimethyl-pyridine (CP), ammonia protectant (N-GD), nitrogen fertilizer synergist (HFJ) and their combination were added into ammonium chloride separately, and nine kinds of stable nitrogen fertilizers were prepared as fertilizer treatment materials. Using no nitrogen fertilizer (CK) and common NH₄Cl (CK-N) as controls, a maize pot experiment was conducted. The soil NH₄⁺-N and NO₃^–-N contents in the seedling, big flare, grain filling and mature stage of maize were determined across all treatments. The biomass, grain yield and N content in maize plant were investigated at maturity. Apparent nitrification rate, nitrification inhibition rate, agronomic efficiency, and partial productivity of the nitrogen fertilizers were calculated.

Results 1) Compared with CK-N treatment, all the nine treatments significantly improved the yields of maize. Among all the nine treatments, HFJ produced the most significant increase in yield and nitrogen absorption efficiency (NAE), which were 3.99 and 4.98 times higher than those in CK-N treatments, and also significantly higher than the other 8 treatments (P < 0.05). Among the five nitrification inhibitor treatments, the best two treatments in maize yields were CP + DMPP and CP + DCD, which were 1.90–2.11 times of that in CK-N treatment. The maize biomass in CP + DMPP was significantly higher than that in CP, but similar with those in DMPP and DCD. The N uptake efficiency of CP + DMPP was significantly higher than those of CP and DMPP (P < 0.05). 2) The soil NH₄⁺-N contents in CP + DMPP and CP + DCD treatments were significantly higher than those in CP, DMPP and DCD, with a significant increase of 2.09–2.42 times (P < 0.05). The soil NO₃^–-N contents and the apparent nitrification rate of black soil in the two treatments were significantly reduced by 24% and 66%–68%, respectively, which were significantly different from those in CP and DCD treatments (P < 0.05). The nitrification inhibition rates of CP + DMPP and CP + DCD at seedling stage were as high as 23.9%–24.3%, which were significantly higher than those of CP and DCD (P < 0.05).

Conclusions In black soil, the nitrogen fertilizer synergist HFJ shows the most efficient effect in increasing the utilization rate of NH₄Cl fertilizer, yield and harvest index of maize. Nitrification inhibitor can significantly and effectively slow down the transformation of ammonium nitrogen to nitrate nitrogen, and simultaneous use of two nitrification inhibitors produces better effect than single one does. From the results, we recommend HFJ or CP + DMPP combination when using NH₄Cl as nitrogen fertilizer in maize production in black soil. The nitrification inhibitor combination of CP + DCD is also a good choice, depending on the situation.