ABSTRACT
Some crops, as cotton, need different pesticide treatments for control of pests and diseases. These compounds reach the soil where the may promote changes in the microbial activities which may affect the nutrient cycling and the soil fertility. The influence of some pesticides was studied on the soil microbial activity of Gley and Red Latosol soils, respectively from the "Instituto Biológico", SP, Brazil, experimental field (in São Paulo) and "Instituto Agronômico" Experimental Station (at Tatuí), all planted with cotton. The studies on the soil microbial activity were evaluated by measurements of the dehydrogenase (DHA) and arylsulfatase activities, by quantification of formazan and p-nitrophenol, respectively formed by reaction of these enzymes. The DHA activity in the Gley soil varied approximately from 90.7 to 218.7 µg formazan g-1 in the untreated subarea, and from 87.7 µg g-1 after treatment with carbaryl, to 258.8 µg g-1 soil after treatment of the treated subarea with monocrotofos. The variation in the amounts of the formazan formed in the Red Latosol from Tatuí was from 33.3 µg g-1 soil in the first inter-cropping period to 103.8 µg g-1 after the application of the mixture methyl parathion + deltametryn. The arylsulfatase activity varied approximately from 0.75 to 9.76 µg p-nitrophenol g-1 in the untreated subarea, and from 3.7 µg g-1 soil after treatment with carbaryl to 11.6 µg g-1 soil also after treatment with monocrotofos. In the Red Latosol from Tatuí, this enzyme activity varied from 0 in the inter-cropping period to 3.81 µg p-nitrophenol g-1 soil after the methyl parathion treatment. It was then verified that pesticides influenced differently the 2 types of soil, by promotion or inhibition of the studied soil enzymes activities.
KEY WORDS:
Bioactivity; microorganisms; environmental impact.
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