Inhibition of Nitrification in Soils

Abstract The effectiveness of 24 compounds proposed as inhibitors of nitrification in soils was studied by determining the effects of 10 ppm (soil basis) of each compound on the amounts of nitrate and nitrite produced when soils treated with ammonium sulfate (200 ppm of ammonium N) were incubated at 30C for 14 days. With the soils used, the average effectiveness of the most potent inhibitors decreased in the order: 2‐chloro‐6‐(trichloromethyl)‐pyridine (N‐Serve) > 4‐amino‐1,2,4‐triazole (ATC) > sodium or potassium azide > 2,4‐diamino‐6‐trichloromethyl‐ s ‐triazine (CL 1580) > dicyandiamide > 3‐chloroacetanilide > 1‐amidino‐2‐thiourea > 2,5‐dichloroaniline > phenylmercuric acetate > 3‐mercapto‐1,2,4‐triazole or 2‐amino‐4‐chloro‐6‐methyl‐pyrimidine (AM) > sulfathiazole (ST) > sodium diethyldithiocarbamate. The other compounds tested (gallic acid, cysteine, cystine, methionine, methionine sulfoxide, methionine sulfone, ethionine, thiourea, 1‐allyl‐2‐thiourea, and 2‐mercapto‐benzothiazole) had little or no effect on nitrification of ammonium in soils under the conditions studied. The effectiveness of the inhibitors studied was markedly affected by soil type, soil temperature, and substitution of urea for ammonium sulfate as the source of nitrifiable nitrogen. Most of the inhibitors were considerably more effective at 15C than at 30 C.