PESTICIDE MOBILITY AND PERSISTENCE IN MICROLYSIMETER SOIL COLUMNS FROM A TILLED AND NO-TILLED PLOT

Pesticide leaching losses under varying tillage systems, especially in sandy soils, is not clearly understood. This study compared the leaching and dissipation of two corn (Zea mays L.) C-14-labeled, insecticides-carbofuran (2,3-dihydro-2,2-dimethyl-7-benzo-furanyl-methylcarbamate) and chlorpyrifos [O,O-diethyl O-(trichloro-2-pyridyl) phosphorothioate]-in sandy soil columns from conventional-moldboard plow (CN) and no-till (NT) tillage plots. Microlysimeters, utilizing intact soil columns from established tillage plots, were used to investigate pesticide mobility and dissipation under simulated field precipitation, drainage, and temperature patterns. Leachate from CN tillage columns receiving C-14-carbofuran contained over two times more of the applied C-14 (17.9%) compared to NT columns (7.9%). The major portion (63%) of C-14-carbofuran residues leached from CN columns was associated with a metabolite (unknown I) compared to 40% for NT columns. Slightly more (4.9% compared to 4.6%) C-14 as parent carbofuran leached from CN columns relative to NT. After 106 d of simulated field conditions, 4.0 and 7.8% of the applied parent C-14-carbofuran was recovered from the soil of CN and NT columns, respectively. Average time to peak C-14-carbofuran residue concentrations were retarded by 12 and 39 d for CN and NT columns, respectively, compared to time to peak concentrations of bromide. Less than 0.2% of the applied C-14-chlorpyrifos leached from the soil columns. Differences in the physical, chemical, and/or biological characteristics between CN and NT tillage columns influenced the dissipation and mobility of carbofuran.