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Tillage and Cover Crop Effects on Saturated and Unsaturated Transport of Fluometuron

Desert Research Inst., Water Resources Center, 755 E. Flamingo Rd., Las Vegas, NV 89119-0040

L. Yunsheng

M. E. Essington and D. D. Tyler

Univ. of Tennessee, Dep. of Plant and Soil Science, Knoxville, TN 37901-1071

H. M. Selim

Louisiana State Univ., Dep. of Agronomy, Baton Rouge, LA 70803

*Corresponding author (gwilson{at}snsc.dri.edu).

ABSTRACT

This study compared flow parameters for no-till (NT) and tilled (T) soils from Louisiana and Tennessee, with hairy vetch (Vicia villosa Roth ssp. villosa) or no winter cover crop, under saturated and unsaturated conditions and the multireaction characteristics of fluometuron [N,N-dimethyl-N'-[3-(trifluoromethyl) phenyl] under unsaturated conditions. Miscible displacement experiments were conducted under saturated flow at a rate of 2.13 cm h^–1, and under unsaturated conditions with a matric head of –50 cm at a flow rate of 0.21 cm h^–1. Preferential flow through these loessial soils was evident by asymmetric breakthrough curves (BTC) under saturated conditions for both NT and T systems. The dispersion coefficients describing the nonreactive BTC under saturated conditions for the NT columns were generally lower than for the T columns. Dispersion was substantially higher for saturated flow, with Peclet numbers nearly an order of magnitude lower than for unsaturated flow. The dispersion coefficients under unsaturated conditions were generally two times larger for NT than T systems. Nonreactive solute transport characteristics for the T-vetch cover systems were similar to NT systems with no cover crop under both saturated and unsaturated conditions. Adsorption was enhanced by NT in Louisiana, whereas adsorption was enhanced by vetch cover in Tennessee columns. Tillage and cover crops did not affect the instantaneous reactivity (K_d), whereas the irreversible rate coefficient (K_irr) was four times higher under the vetch system than the no-cover system. The forward and backward kinetic adsorption coefficients were two times higher under NT than T systems.

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Received for publication February 18, 1997.

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