Effects of phosphoroamides on nitrification, denitrification, and mineralization of organic nitrogen in soil

Abstract

Recent work has shown that several phosphorodiamides and phosphorotriamides are potent inhibitors of soil urease activity and have potential value for retarding hydrolysis of fertilizer urea in soil. The effects of nine of these compounds on nitrification, denitrification, and mineralization of organic nitrogen in soil were studied by determining the influence of different amounts of each compound on (1) the amounts of (nitrate + nitrite)-N produced when soils were incubated aerobically after treatment with ammonium sulfate, (2) the amounts of nitrate-N lost and the amounts of (nitrite + N2O + NO + N2)-N produced when soils were incubated anaerobically after treatment with potassium nitrate, and (3) the amounts of inorganic N produced when soils were incubated aerobically after treatment with alanine. The compounds studied were phenylphosphorodiamidate, N-(diaminophosphinyl)-cyclohexylamine, N-benzyl-N-methyl phosphoric triamide, trichloroethyl phosphorodiamidate, diethyl phosphoric triamide, dimethyl phosphoric triamide, N-butyl phosphorothioic triamide, N-fluoro-N-(diaminophosphinyl)benzamide, and N-phenylphosphoric triamide. The data obtained showed that only trichloroethyl phosphorodiamidate had a significant inhibitory effect on nitrification when applied at the rate of 5 or 10 .mu.g g-1 soil and that only trichloroethyl phosphorodiamidate and N-butyl phosphorothioic triamide has an appreciable inhibitory effect when applied at the rate of 50 or 100 .mu.g g-1 soil. None of the phosphoroamides studied inhibited denitrification of nitrate or mineralization of organic nitrogen when applied at the rate of 10 or 50 .mu.g g-1 soil.