Effects of parathion and malathion on transformations of urea and ammonium sulfate nitrogen in soils

A study of the effects of malathion and parathion applied at 10 and 50 g/g of soil on transformations of urea and (NH4)2SO4–N in a sandy loam showed that the insecticides retarded urea hydrolysis as well as nitrification of urea and (NH4)2SO4–N. At 50 parts/106 rate of the insecticides, inhibition of urea hydrolysis ranged from 44 to 61% after 0.5 week and from 7 to 21% after 3 weeks of application. The insecticides inhibited the conversion of NH4 + to NO2 – without appreciably affecting the subsequent oxidation of NO2 – to NO3 – –N. This resulted in accumulation of higher amounts of NH4 +–N in soil samples treated with ammonium sulfate or urea N. The results suggest that transformations of urea and NH4 + fertilizers in soils may be influenced by the amount of organophosphorus insecticide present and this may affect plant nutrition and fertilizer use