Denitrification in soil: Effects of insecticides and fungicides

Abstract

The effects of seven insecticides and six fungicides on denitrification of nitrate in soils were studied by determining the effects of 10 and 50μgg −1 soil of each pesticide on the amounts of nitrate lost and the amounts of nitrite, N 2O and N 2 produced when soil samples were incubated anaerobically after treatment with nitrate. The insecticides used were lindane, fenitrothion, fonofos, malathion, phorate, terbufos and carbofuran. The fungicides used were mancozeb, maneb, thiram, benomyl, captan and terrazole. None of the insecticides studied had a significant effect on denitrification when applied at the rate of 10 μgg −1 soil. When applied at the rate of 50μgg −1 soil, lindane, fonofos and malathion enhanced denitrification in the three soils studied, whereas fenitrothion, phorate, terbufos and carbofuran either had no appreciable effect on denitrification in these soils, or enhanced denitrification in at least one of the soils. None of the fungicides studied had an appreciable effect on denitrification when applied at the rate of 10μgg −1 soil, but thiram increased the ratio of N 2 to N 2O in the gaseous products of denitrification. Captan inhibited denitrification in two of three soils studied when applied at the rate of 50μgg −1 soil. The other five fungicides either had no significant effect on denitrification, or enhanced denitrification, when applied at this rate. Reports that maneb, thiram and terrazole inhibit denitrification in soil were not confirmed.