STUDY OF THE RELATION BETWEEN CARBOFURAN DEGRADATION AND MICROBIAL OR PHYSICOCHEMICAL CHARACTERISTICS OF SOME FRENCH SOILS

In France, corn rootworm (Agriotes sp.) is controlled by applying insecticides such as carbofuran to the soil. In recent years, the failure of carbofuran to control this pest has been observed in the south-west area of France in continuous corn cropping. A soil survey was conducted in order to determine the main factors which could influence carbofuran degradation in various soils. Degradation estimates were based on measurement of the release of [C-14]carbon dioxide from [carbonyl-C-14]carbofuran. The enhanced degradation of carbofuran observed in laboratory conditions corresponded to the growth of micro-organisms able to use carbofuran as sole carbon and nitrogen source. The size of this microbial population and the rates of carbofuran degradation were higher in the samples taken from plots with a history of carbofuran use than in samples from previously untreated plots. Abiological degradation was only observed in alkaline soil conditions. Statistical analyses showed that carbofuran-degrading activity was not related to any particular pedological characteristics.