Inhibition of soil urease by organophosphorus insecticides

Abstract

The effect of three organophosphorus insecticides on soil urease was examined. Inhibition of urea hydrolysis, some 60 days after application of 1000 parts/106 of insecticide to a sandy clay loam, approached 40% (accothion) and exceeded 50% in the case of malathion and thimet. Similar inhibitory effects were recorded using a silt loam soil with which 200 parts/106 application also produced inhibition ranging from 14% (accothion) to 23% (thimet) after 10 days. With lower concentrations of insecticide (50 parts/106) inhibition, though again significant, was of a more ephemeral nature. All three insecticides, at a concentration of 1000 parts/10+6, prevented almost any hydrolysis of urea by jack bean urease. Ureolytic microorganisms, isolated from the soils under investigation, were inhibited by the organophosphates to a greater or lesser extent but the development of tolerance was common. It is suggested that the application of insecticides to control soil-borne insect pests may be a factor in determining the efficiency of urea fertilizer mineralization. © 1976.