Herbicide Runoff from Upland Piedmont Watersheds—Data and Implications for Modeling Pesticide Transport

Abstract

Runoff and persistence of selected herbicides were studied on four small Piedmont watersheds in Georgia during four growing seasons. This is part of a study designed to provide data for developing and testing mathematical models for agricultural chemical transport. Seasonal runoff losses were determined relative to watershed management, herbicide type and persistence, mode of application, and time of runoff in relation to application timing. Seasonal losses were usually < 2% of the application, unless large runoff volumes were generated shortly after application. Average storm herbicide concentrations in runoff were correlated with herbicide concentrations at the 0‐ to 1‐ cm depth increment of the watershed soils at the time of runoff. Paraquat concentrations in runoff (predominantly sediment associated) were well correlated and positive with the product of soil herbicide concentration and sediment in runoff. Equations describing soilbased herbicide transfer to runoff were power functions with exponents near unity with the form: Y = a xb. Simple relationships such as those developed in this study along with hydrology and erosion/sediment models may he useful in predicting pesticide runoff potential when assessing relative impacts of management decisions. The next step would be to describe key management practices in terms of these coefficients and exponents.

Effects of subsurface drip irrigation rates and furrow irrigation for cotton grown on a vertisol on off-site movement of sediments, nutrients and pesticides

“…as a pre-planting application was applied only in the second year and its movement was limited solely to furrow irrigation. The furrow runoff carried more than 10% of the applied trifluralin which contrasts with data of Leonard et al (1979) that showed only a small proportion of the applied trifluralin in run-off. Total trifluralin loss in run-off was strongly related to run-off volume rather than to concentrations in that run-off because the soil sorption index for trifluralin is very high (8000 Koc) (Silburn and Glanville, 2002).…”

Validation of the exposure assessment for veterinary medicinal products

“…These models have initially been developed for herbicides. They describe non-linear relationships, with an extraction coefficient representing removal of the pesticide from the top 1 cm soil layer and an exponent representing reductions in the extraction potential with ageing (Leonard et al, 1979 andSouthwick et al, 2003). Additional alternatives are the use of total losses, which may be implemented through probabilistic models (Pablos et al, 1998).…”

Heptachlor and Its Metabolite: Accumulation and Degradation in Sediment

“…Since soil organic matter is the primary soil constituent responsible for sorption of non-ionic pesticides, a sorption constant based on only the organic carbon present (Koc, dm 3 kg -1 ) can be used to assess pesticide mobility, Koc = Kd/oc. Where Kd is a measure of the extent of pesticide sorption by the soil, and oc is the fraction of the organic C present in the soil [14]. A sorption constant expressed in this manner is dependent only on the pesticide and is essentially independent of soil type.…”