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EFFECT OF 3,5-DIMETHYLPYRAZOLE AND NITRAPYRIN ON NITRIFICATION UNDER HIGH SOIL TEMPERATURE

R. ALI¹, J. IQBAL², G.R. TAHIR¹ AND T. MAHMOOD¹*

Abstract: Experiments were conducted under laboratory conditions to elucidate the effect of 2 nitrification inhibitors viz., 3,5-dimethylpyrazole (DMP) and nitrapyrin on nitrification of (NH4)2SO4 in soil incubated at 35°C. When these inhibitors were applied at rates generally recommended for agricultural use (DMP at 0.225–0.45 mg kg–1; nitrapyrin at 0.25–0.50 mg kg–1), almost all NH4+-N disappeared within a week in the soil treated with DMP, whereas it took 2 weeks in the presence of nitrapyrin. When DMP application rate was increased in the range of 0.225–3.6 mg kg–1, NH4+-N disappeared within 2 weeks in the soil receiving DMP upto 0.90 mg kg–1, whereas it took 3 weeks with DMP applied at 1.8–3.6 mg kg–1. In another experiment, nitrapyrin application rate was increased in the range of 1.04–52 mg kg–1 using a commercial product viz., N-Serve 24 (22.2% active ingredient). In contrast to the unamended control where all NH4+-N disappeared within a week, nitrification was delayed particularly with higher concentrations of nitrapyrin and only 50 and 8 % of the NH4+-N was nitrified in 4 weeks with nitrapyrin applied at 8.32 and 26 mg kg–1, respectively. Results suggested that DMP and nitrapyrin applied at rates generally recommended for agricultural use under moderate climate may not be effective under high summer temperatures prevailing in Pakistan. Application of high concentrations of these chemicals to achieve the desired effects under warm agro-climate may not be economically feasible. Besides, higher concentrations of these nitrification inhibitors can be phytotoxic or adversely affect the activities of soil microflora.

¹Nuclear Institute for Agriculture & Biology, PO Box 128, Jhang Road, Faisalabad 38000, Pakistan

²School of Biological Sciences, University of the Punjab, Quaid-e-Azam Campus, Lahore 54590, Pakistan

*Corresponding author E-mail: tmahmood114@yahoo.com