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Title: TILLAGE EFFECT ON MACROPOROSITY AND HERBICIDE TRANSPORT IN PERCOLATE

Author
item Malone, Robert - Rob
item Logsdon, Sally
item Shipitalo, Martin
item WEATERINGTON-RICE, JULIE - BENNETT AND WILLIAMS
item Ahuja, Lajpat
item Ma, Liwang

Submitted to: Geoderma
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2003
Publication Date: 9/19/2003
Citation: MALONE, R.W., LOGSDON, S.D., SHIPITALO, M.J., WEATERINGTON-RICE, J., AHUJA, L.R., MA, L. TILLAGE EFFECT ON MACROPOROSITY AND HERBICIDE TRANSPORT IN PERCOLATE. GEODERMA. 2003. v. 116. p. 191-215.

Interpretive Summary: Pesticides move to tile drains and shallow groundwater mainly through macropores (root channels, worm burrows, cracks in soil, etc). The effect of tillage on macropores and pesticide movement, however, is uncertain. Therefore, we investigated the effect of tillage on herbicide movement through macropores that can transmit water. Our results suggest that the same quantity of macropores are conduits for water and herbicides under both tilled and no-till conditions. Also, the time between rainfall initiation and flow into macropores was less under no-till than under tilled soil. This results in higher pesticide concentration in macropore flow than under tilled soil. These results are key to understanding pesticide movement into the environment and will help in designing farming practices that reduce pesticide concentrations in streams and groundwater. This work will help scientists as well as decision-makers and farmers reduce pesticide contamination in the environment.

Technical Abstract: We investigated the effect of tillage on herbicide leaching through hydraulically active macropores. Methods used were: quantify hydraulically active macropores >0.05 cm radius for structured Midwestern subsurface soils (15 to 35 cm deep); measure the number of hydraulically active macropores and the timing of initial percolate from moldboard plowed (MP) and no-till (NT) undisturbed soil blocks where atrazine, alachlor, and rainfall were applied to two different soils; and simulate alachlor and atrazine transport through the undisturbed soil blocks using the Root Zone Water Quality Model (RZWQM). Tension infiltrometer data revealed an average of 0.021 active macropores per cm**2 for NT and 0.019 cm**-2 for MP at 15 to 35 cm deep; the undisturbed soil blocks revealed the number of percolate producing macropores at 30 cm (nmacro) was not significantly different between MP and NT, the time of initial percolate breakthrough at 30 cm was significantly different between MP and NT (p<0.001), and nmacro was significantly different between soils (p<0.001). Regression analysis on the undisturbed silt loam soil blocks revealed that herbicide concentration in percolate was influenced by nmacro (cm**-2) and the time of initial percolate breakthrough (min.) (R**2 = 0.87 for alachlor and 0.85 for atrazine). Using half of measured nmacro and calibrating soil parameters to accurately simulate timing of percolate arrival and percolate amount resulted in accurate RZWQM simulated herbicide concentrations in percolate at 30 cm (within a factor of 2). This suggests that: nmacro may not differ between till and no- till, and timing of flow through macropores during a storm may be a key mechanism for pesticide transport differences between till and no-till.