Inhibitory effects of fungicides on hydrolysis of urea and nitrification of urea nitrogen in soil

The influence of 1 and 50 mg active ingredient (Al) kg(-1) soil of 17 fungicides on transformations of urea nitrogen in soil was studied by determining the amounts of urea hydrolysed and the amounts of nitrate and nitrite produced when samples of two coarse-textured and two fine-textured soils were incubated aerobically for various times after treatment with urea When applied at the rate of 1 mg AI kg(-1) soil, anilazine, benomyl, captan, chloranil, mancozeb and thiram retarded urea hydrolysis in the two coarse-textured soils and maneb retarded urea hydrolysis in all four of the soils used. Most of the fungicides tested retarded nitrification of urea nitrogen in the two coarse-textured soils when applied at the rare of 1 mg Al kg(-1) soil, but only etridiazole markedly retarded nitrification of urea nitrogen in all of the soils used when applied at this rate. When the fungicides were applied at the rate of 50 mg AI kg(-1) soil, anilazine, captan, chloranil, fenaminosulf, folpet, maneb, mancozeb and thiram retarded urea hydrolysis in the four soils studied, and all fungicides tested except chloroneb, fenarimol and iprodione retarded nitrification of urea nitrogen in these soils. One-way analysis of variance and correlation analyses indicated that the inhibitory effects of the 17 fungicides tested on nitrification of urea nitrogen in soil increased with decrease in the organic-matter content and increase in the sand content of the soil.