CROP RESIDUE EFFECTS ON THE LEACHING OF SURFACE-APPLIED CHEMICALS

Unknown effects of surface crop residues on interception, subsequent w ash-off, and movement of herbicides through soil are concerns associat ed with no-tillage agriculture. To address these concerns, 12 undistur bed columns of a Clarion (fine-loamy, mixed, mesic Typic Hapudoll) soi l were obtained from a no-till corn (Zea mays L.) field following harv est. Saturated hydraulic conductivity (K-sat), Cl- break-through, and drainable porosity were measured and used to group the columns into th ree blocks (high, medium, and low K-sat values). Corn residue was plac ed on the surface at rates of 0, 473, 946, and 1419 kg ha(-1). Atrazin e hyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and CaCl2 solutio ns were surface applied to the columns, and 24 h later a sprinkling de vice was used to apply CaSO4 at a rate of 5 cm h(-1). Effluent drainin g from the columns was collected and analyzed for Cl- and atrazine. Gr eater amounts of atrazine were recovered with the first 5.0 cm of drai nage in the 100%-residue columns than with the zero-residue columns fo r the high and medium-K-sat blocks. Differences in mass of atrazine re covered were greater in high-K-sat than in medium-K-sat columns. A tre nd indicating more recovery with less drainage for the high-residue tr eatment was not apparent for the low-K-sat columns. The time to peak a trazine concentrations decreased as crop residue levels increased for the higher-K-sat columns, but not for the low-K-sat columns. With 100% residue cover, the medium-and high-K-sat columns demonstrated two pea ks in Cl- and atrazine concentrations. This may indicate two pathways for the Cl- and atrazine movement through these columns; perhaps indic ating the surface-applied chemical that was not intercepted by crop re sidue was moving more slowly through the soil matrix.