Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2007
Publication Date: 2/15/2008
Citation: Locke, M.A., Zablotowicz, R.M., Reddy, K.N., Steinriede Jr, R.W. 2008. Tillage management to mitigate herbicide loss in runoff under simulated rainfall conditions. Chemosphere. 70:1422-1428. Interpretive Summary: It has been demonstrated that conservation management can reduce negative impacts of sediment and runoff on quality of receiving waters. The effects of conservation management on pesticide fate are not as well understood, because the pesticide class is comprised of numerous chemical compounds (e.g., herbicides, fungicides) with diverse properties and reactions. Therefore, many mechanisms can account for pesticide fate. A microplot study was conducted to evaluate the effect of tillage on loss of the herbicides alachlor and chlorimuron in runoff. Sediment loss was less on untilled soils, but effects on the two herbicides differed. Alachlor has a greater affinity for organic matter and is less water soluble, while chlorimuron is more water soluble, especially at higher pH. Alachlor loss in runoff was lower in untilled than in tilled soil, while chlorimuron runoff losses were higher in untilled soil. These results are of interest to regulatory and other agencies and the pesticide industry as part of overall assessments of contributions of management to environmental improvement.
Technical Abstract: Conservation tillage reduces soil loss in cultivated cropland because plant residues protect the soil, but the effects of conservation tillage on the movement of pesticides in surface runoff are not as straightforward. We assessed effects of soil disturbance on surface runoff loss of chlorimuron and alachlor from runoff trays (2.73 m2) containing Bosket sandy loam (1.2% slope). Soil was either disturbed by raking and kept bare or was not disturbed, and existing plants were allowed to die back and decompose over several months. In the chlorimuron study, plant residues on the surface of undisturbed plots were originally derived from smooth pigweed (Amaranthus hybridus L.) and large crabgrass (Digitaria sanguinalis L.). In the alachlor study, plant residues in undisturbed plots were from a mixture of Italian ryegrass (Lolium multiflorum Lam.) and crimson clover (Trifolium incarnatum L.). Rainfall (2.5 cm, 20 min) was simulated one day after alachlor (2.8 kg ha-1) or chlorimuron (54 g ha-1) application, and runoff was collected in 1-L fractions. Runoff fractions were analyzed for herbicide using enzyme-linked immunosorbent (ELISA) assay and sediment loss. Total alachlor lost from bare plots was greater than that in residue plots (4.5% vs. 2.3%, respectively). More than one-third of total alachlor loss from bare plots occurred in the first liter of runoff, while residue plots had less runoff volume (14 L in residue vs. 29 L in bare) and more even distribution of alachlor concentration in the runoff during rainfall simulation and subsequent runoff period. In contrast, more chlorimuron was removed from residue plots than bare plots (23% vs. 3%) even though water runoff was lower in the residue plots (29 L vs. 38 L). This was attributed to the more polar nature of chlorimuron which may have inhibited sorption interaction with surface plant residues.