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Crop Residue Effects on the Leaching of Surface-Applied Chemicals

Dep. of Agronomy and Dep. of Agricultural and Biosystems Engineering, Iowa State Univ., Ames, IA 50011.

^* Corresponding author. (rhorton{at}iastate.edu).

ABSTRACT

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 CaCl₂ solutions were surface applied to the columns, and 24 h later a sprinkling device was used to apply CaSO₄ 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.

Journal Paper no. J-15530 of the Iowa Agric. and Home Econ. Exp. Stn. Ames, IA. Project no. 2556. Partial support for this study was provided by Management Systems Evaluation Area Project.

Received for publication January 11, 1994.