EFFECT ON MICROORGANISMS AND PERSISTENCE OF FIELD-APPLIED CARBOFURAN AND DYFONATE IN A HUMIC MESISOL

Abstract

Banded and broadcast applications of carbofuran at 4.48 kg a.i.(active ingredient)/ha, and a banded application of Dyfonate at 2.24 kg. a.i./ha were made to field plots on an organic soil on which onions and lettuce were grown. About 60% of the Dyfonate initially present, and more than 90% of the carbofuran disappeared in 125 days. The differences caused in the size of microbial population by Dyfonate were mostly marginal, ambivalent and transient. However, both carbofuran applications resulted in about 100 to 300% increases in bacterial plus actinomycetal populations spanning 3 samplings over 2 mo. CO2 evolution was also increased for a longer period by carbofuran additions. The fungal population was altered only slightly. NO3-N, NH4-N and H2O-soluble PO4 levels were not changed substantially due to the insecticide treatments in this organic soil.