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 trea tment with urea When applied at the rate of 1 mg AI kg(-1) soil, anila zine, benomyl, captan, chloranil, mancozeb and thiram retarded urea hy drolysis in the two coarse-textured soils and maneb retarded urea hydr olysis in all four of the soils used. Most of the fungicides tested re tarded 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 th e rate of 50 mg AI kg(-1) soil, anilazine, captan, chloranil, fenamino sulf, folpet, maneb, mancozeb and thiram retarded urea hydrolysis in t he four soils studied, and all fungicides tested except chloroneb, fen arimol 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 nitrificat ion of urea nitrogen in soil increased with decrease in the organic-ma tter content and increase in the sand content of the soil.