Effects of nitrification inhibitors on denitrification of nitrate in soil

Abstract

The influence of 28 nitrification inhibitors on denitrification of nitrate in soil was studied by determining the effects of different amounts of each inhibitor on the amounts of nitrate lost and the amounts of nitrite, N2O and N2 produced when soil samples were incubated anaerobically after treatment with nitrate or with nitrate and mannitol. The inhibitors used included nitrapyrin (N-Serve), etridiazole (Dwell), potassium azide, 2-amino-4-chloro-6-methylpyrimidine (AM), sulfathiazole (ST), 4-amino-1,2,4-triazole(ATC),2,4-diamino-6-trichloromethyl-s-triazine (CL-1580), potassium ethylxanthate, guanylthiourea (ASU), 4-nitrobenzotrichloride, 4-mesylbenzotrichloride, sodium thiocarbonate (STC), phenylmercuric acetate (PMA), and dicyandiamide (DCD). Only one of the nitrification inhibitors studied (potassium azide) retarded denitrification when applied at the rate of 10 μg g−1 soil, and only two (potassium azide and 2,4-diamino-6-trichloromethyl-s-triazine) inhibited denitrification when applied at the rate of 50 μg g−1 soil. The other inhibitors either had no appreciable effect on denitrification, or enhanced denitrification, when applied at the rate of 10 or 50 μg g−1 soil, enhancement being most marked with 3-mercapto-1,2,4-triazole. Seven of the inhibitors (potassium azide, sulfathiazole, potassium ethylxanthate, sodium isopropylxanthate, 4-nitrobenzotrichloride, sodium thiocarbonate, and phenylmercuric acetate) retarded denitrification when applied at the rate of 50 μg g−1 soil to soil that had been amended with mannitol to promote microbial activity. Reports that nitrapyrin (N-Serve) and etridiazole (Dwell) inhibit denitrification when applied at rates as low as 0.5 μg g−1 soil could not be confirmed. No inhibition of denitrification was observed when these compounds were applied at the rate of 10 μg g−1 soil, and enhancement of denitrification was observed when they were applied at the rate of 50 or 100 μg g−1 soil.