Evaluation of some nitrification inhibitors at different temperatures under laboratory conditions

Effect of eight compounds on nitrification of the applied (NH4)(2)SO4 was studied in two soils incubated at high (35 degrees C) and moderate (16 degrees C) temperatures. The tested compounds included: 1H-benzotriazole; 4-amino-1,2,4-triazole; benzothiazole; 3-methylpyrazole-1-carboxamide; 4-bromo-3-methylpyrazole; pyrazole; lignosulfonic acid, molecular weight 52000, 6% S; and lignosulfonic acid, molecular weight 12000, 2% S. In the absence of inhibitors, nitrification of the applied ammonium was complete within one week at 35 degrees C, whereas it took two to three weeks at 16 degrees C. At 35 degrees C, ATC was the most effective compound causing 44-71% inhibition up to four weeks when applied at 10 mg kg(-1). The inhibitory effect of ATC increased with increasing application rate to 30 mg kg(-1) (92-94% inhibition for four weeks). Although another compound viz. PZ applied at 10 mg kg(-1) was also effective at 35 degrees C, the inhibitory effect persisted up to three weeks (44-48% inhibition). At 16 degrees C, six of the test compounds (BTr, ATC, BTh, MPC, BMP and PZ) effectively inhibited nitrification at least up to four weeks. At 16 degrees C also, ATC was the most effective compound causing 84-90% inhibition for four weeks when applied at 10 mg kg(-1). The results suggested that ATC can be a potential nitrification inhibitor for agricultural use under summer as well as under winter soil temperatures prevailing in the Indo-Gangetic Plains of the South Asia.