Crop Residue Effects on the Leaching of Surface‐Applied Chemicals

Unknown effects of surface crop residues on interception, subsequent wash‐off, and movement of herbicides through soil are concerns associated with no‐tillage agriculture. To address these concerns, 12 undisturbed columns of a Clarion (fine‐loamy, mixed, mesic Typic Hapudoll) soil were obtained from a no‐till corn ( Zea mays L.) field following harvest. Saturated hydraulic conductivity ( K sat ), Cl − breakthrough, and drainable porosity were measured and used to group the columns into three blocks (high, medium, and low K sat values). Corn residue was placed on the surface at rates of 0, 473, 946, and 1419 kg ha −1 . Atrazine [6‐choloro‐ N ‐ethyl‐ N′ ‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] and CaCl 2 solutions were surface applied to the columns, and 24 h later a sprinkling device was used to apply CaSO 4 at a rate of 5 cm h −1 . Effluent draining from the columns was collected and analyzed for Cl − and atrazine. Greater amounts of atrazine were recovered with the first 5.0 cm of drainage in the 100%‐residue columns than with the zero‐residue columns for the high and medium‐ K sat blocks. Differences in mass of atrazine recovered were greater in high‐ K sat than in medium‐ K sat columns. A trend indicating more recovery with less drainage for the high‐residue treatment was not apparent for the low‐ K sat columns. The time to peak atrazine 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 peaks in Cl − and atrazine concentrations. This may indicate two pathways for the C − and atrazine movement through these columns; perhaps indicating the surface‐applied chemical that was not intercepted by crop residue was moving more slowly through the soil matrix.