ABSTRACT:
Soils that naturally have a significant runoff component because of low permeability, such as claypans or steep slopes, are especially susceptible to herbicide losses in runoff. For these soils, seasonal losses as impacted by management practices are not well quantified. The objectives of this study were to evaluate the effect of three cropping systems on herbicide loss in surface runoff and develop a model that calculates herbicide concentration. Cropping System 1 (CS1) was a mulch tillage corn-soybean rotation system with herbicides surface applied then incorporated. Cropping System 2 (CS2) was a no-till corn-soybean rotation system with herbicides surface applied and not incorporated. Cropping System 5 (CS5) was a no-till corn-soybean-wheat rotation system with split herbicide application in 1997 and 1999 and no incorporation. The study was conducted on 0.37 ha (0.92 ac) plots equipped with flumes and automated samplers. During each runoff event, runoff volumes were measured, and water samples were collected at equal flow increments and analyzed for atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine] and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethy/acetamide]. Averaged over years, atrazine and metolachlor losses from CS2 were 2.2 and 1.6 times those from CS1, respectively. Atrazine loss to surface runoff from CS1, CS2, and CS5 accounted for 1.6, 2.5, and 5.7% of the total atrazine applied, respectively. Metolachlor loss to surface runoff accounted for 1.8, 2.0, and 2.0% of the total applied for the three cropping systems. Herbicide concentrations were extremely high in the first runoff event measured after application, particularly when it occurred within a few days after application. A generalized model was developed to account for the effects of time after application, runoff volume, and application rate on herbicide concentration in runoff. Overall, the study showed that accounting for incorporation, split application, runoff volume, and timing of runoff events relative to the day of application can increase the confidence in calculations of the amount of herbicide transported to surface runoff.
Footnotes
Fessehaie Ghidey, R.N. Lerch, Newell R. Kitchen, E. Eugene Alberts, and E. John Sadler work for the U.S. Department of Agriculture Agricultural Research Service in the Cropping Systems and Water Quality Research Unit in Columbia, Missouri. P.E. Blanchard works for the Missouri Department of Conservation in Columbia, Missouri.
- Copyright 2005 by the Soil and Water Conservation Society