Inhibition of DCD, DMPP and Nitrapyrin on soil nitrification and their appropriate use dosage

ObjectivesNitrification inhibitors are effective in regulating the transformation of soil nitrogen and the community structure of microbes which involve in the N nitrification process. Incubation and pot experiments were conducted to compare nitrification effects of 3 common used nitrification inhibitors, and to study the dosage for practical use in calcareous soil.

MethodsThe incubation experiment was carried out in a plant growth chamber at 25℃ in dark condition, and the pot experiment was conducted in greenhouse. The tested three inhibitors were dicyandiamide (DCD), 3,4-dimethylpyrazole phosphate (DMPP) and chloro-6-trichloromethyl-pyridine (nitrapyrin). The dosage of DCD and DMPP designed as 0 (CK), 1.0%, 2.0%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 6.0% and 7.0% of the N addition, those of nitrapyrin were 0, 0.1%, 0.125%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45% and 0.5%. N 0.50 g per kg of dry soil was added in pot experiment, and the dosages of three inhibitors were all 5%, 1%, 0.648% of the N addition. The nitrate inhibition rate and the biomass of pakchoi were investigated; the soil microbial community structures of AOA and AOB were analyzed using the method of denaturing gradient gel electrophoresis (DGGE).

ResultsSoil nitrification was significantly inhibited by DCD, DMPP and nitrapyrin (P＜0.05). Compares with the CK, soil NH₄⁺-N concentrations were increased by 46.2-256.1 mg/kg with DCD, by 291.8-376.7 mg/kg with DMPP and by 3.68-372.9 mg/kg with nitrapyrin, respectively. The nitrification inhibition rates were 49.3%-79.4% with DCD and 96.4%-99.4% with DMPP. The DCD addition exhibited an obvious dose effect, namely, the nitrification inhibition rates were increased significantly with DCD dose increasing, the DMPP did not in the addition range of 1.0%-7.0%, Although nitrapyrin only showed dose response in low concentrations from 0.1% to 0.2%, the inhibition rate had reached 98.9%-99.9% when nitrapyrin concentration raised over 0.25%. The inhibition ability followed the order of nitrapyrin≥DMPP>DCD. A significant impact of all three NIs on AOA and AOB community structure alteration was found, but there was no significant difference among the three inhibitors. The pakchoi above-ground weight, the contents of Vitamin C and amino acid were significantly improved by DCD, DMPP and nitrapyrin addition (P＜0.05), with the increase of pakchoi biomass of 12.7% with DCD, 11.1% with DMPP and 17.6% with nitrapyrin, respectively.

ConclusionBriefly, DCD, DMPP and nitrapyrin showed significant role in retarding nitrification in calcareous soil and exerted an obvious influence on AOA and AOB community structure (P＜0.05). Comparatively, nitrapyrin was superior over DMPP and DCD on the soil inhibition, and the addition dose of 0.25% based on pure N was recommended for nitrapyrin application.