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Microbiological Effects and Persistence of Some Pesticide Combinations in Soil¹

ABSTRACT

Zineb, parathion, DDT, and Furadan were applied alone and in combination to field plots, with times and rates of application approximating current agronomic practice for the growth of shade-leaf tobacco in the area of Quincy, Florida. Persistence of the pesticides in the soil and possible effects of the pesticides on relative microbial numbers and nitrification were monitored at 2-week intervals over a period of 16 weeks. Relative numbers of bacteria and actinomycetes in all treatments failed to differ significantly from the untreated control. Fungi increased significantly (5% level) in the parathion + DDT + zineb treatment. There were no other significant differences in microbial numbers. Nitrification, as indicated by levels of NO₃-N, showed no significant difference due to treatments when compared to the control at the 5% level. Parathion applied as a single dose was present in the soil in significantly higher amounts initially when compared with treatments where parathion was applied on a weekly basis. This difference disappeared after 6 weeks. There were no other significant differences in pesticide persistence in the soil.

Key Words: parathion • DDT • zineb • Furadan • nitrification

¹ Contribution from the Departments of Soils and Food Science, Univ. of Florida, Gainesville, and Agricultural Research and Education Center, Quincy, Journal Series 4346.

² Assistant Professor and Professor, Dep. of Soils, Univ. of Florida, Gainesville, 32601; Assistant Professor, Pesticide Res. Lab., Dep. of Food Science, Univ. of Florida, Gainesville; Associate Professor and Assistant Professor, Agr. Res. and Educ. Cent., Quincy, 32351, respectively.

Received for publication March 6, 1972.