Insecticide Depth in Soil—Effect on Soybean Uptake in the Greenhouse

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Abstract
The influence of DDT, dieldrin, and endrin placement depth in soil on their plant uptake and translocation was investigated. In a greenhouse study, soybeans were grown for 75 days in soil columns containing a 1‐cm layer of 20 ppm 14C‐insecticide‐treated soil placed at either 1–2, 16–17, or 31–32 cm deep (depths A, B, and C, respectively) within the column. Radioactivity in root sections showed that all three insecticides were absorbed and translocated both basipetally and acropetally. Maximum mean residues in roots (DDT, 14.9; dieldrin, 29.1; endrin, 29.5 ppm air‐dry basis) always resulted from placement at depth A.Maximum DDT (<0.01 ppm), dieldrin (0.68 ppm), and endrin (1.20 ppm) residues in total aerial organs resulted from depth A also. Residues decreased strikingly as placement depth increased. The B depth resulted in mean aerial residues amounting to 6.8% (dieldrin) or 15.0% (endrin) of those resulting from A, while C depth resulted in mean aerial residues of only 0.6% (dieldrin) or 6.7% (endrin) of those from depth A. Only trace amounts of DDT residues resulted from depths B and C.Since uptake was affected by insecticide placement depth, prediction of crop residues based on soil residues must include a consideration of residue location in soil. Results suggest that deep plowing of insecticide‐containing soil could be used to reduce residues in crop plants.

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