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Relationship Between Herbicide Concentration in Percolate, Percolate Breakthrough Time, and Number of Active Macropores

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Paper number  032179,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.13796) @2003
Authors:   R. W. Malone, M. J. Shipitalo, D. W. Meek
Keywords:   Preferential flow, Multiple parameter regression, Herbicide leaching, RZWQM, Alachlor, Atrazine

Identification of the major factors affecting herbicide transport through macropores improves our understanding of preferential flow and helps in the development and use of macropore flow models such as the Root Zone Water Quality Model (RZWQM). Recent research suggests that macropore flow breakthrough time (bt) and the number of percolate producing macropores (nmacro) affect herbicide concentration in percolate (hc). Therefore, we investigated the effect of bt and nmacro on hc during the first storm after application using multiple regression and partial correlation. Observed data were from five different leaching experiments that included five soil types and two tillage types (no-till and moldboard plow). Regression was used to develop a model to predict herbicide concentration (hc) in preferential flow at 30 cm during the first rainfall after application using data from the five studies. The ln(hc) in macropore flow at 30 cm was related to bt (min.) at 30 cm, ln(nmacro) at 30 cm, herbicide type (alachlor or atrazine), and herbicide application rate (R2 = 0.96). Partial correlation confirmed the relationship between ln(hc) and bt (P<0.0001; r=-0.77) and ln(nmacro) (P<0.0001; r=-0.46). A single variable sensitivity analysis on the regression equation suggested that the observed range of bt (1.4 to 25 min.) results in an eight-fold change in atrazine herbicide concentration (4.0 to 0.48 mg L-1). Clearly breakthrough time during the first storm after application affects herbicide transport.

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