|Banks, Philip - MARATHON AG. CONSULTING|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: April 20, 2007
Publication Date: March 7, 2008
Citation: Koskinen, W.C., Banks, P.A. 2008. Soil movement and environmental fate of triazine herbicides. In: LeBaron, H.M., Burnside, O.C., J. McFarland, editors. The Triazine Herbicides. Amsterdam, The Netherlands:Elsevier Science. p. 355-385. Technical Abstract: Although the majority of an applied triazine herbicide remains in the surface soil where it controls weeds while degrading, soil movement and persistence has been well studied and documented. A variety of factors affect triazine runoff, including method of application, soil properties, type of tillage, and environmental conditions. Estimates of triazine amounts in runoff from agricultural fields vary widely, with the highest concentrations occurring in the first two months after application. In most field leaching studies, which are typically limited to depths <2 m, triazines are retained and degraded in the top 50 cm of surface soil. Amounts of triazines detected in subsurface drainage water are typically lowabout 0.1% of the triazine applied to crops. Triazine persistence is usually characterized in terms of the time it takes for 50% of the triazine to either degrade (t1/2) or dissipate (DT50). Alues of t1/2 or DT50 range from 14 to 112 days, with a mean t1/2 or DT50 of 36 days ± 25 days. In many cases, triazine dissipation has been shown to be biphasic, not first-order. For instance, when applied in spring, initial rapid degradation occurs during the first two months after application, followed by slower degradation in the dry summer and cold fall and winter. Triazines can persist at low concentrations for long periods after application; however, they do not accumulate in soil after long-term use. Thus, triazine movement and persistence are influenced by many factors, the interactions of which are not always easy to predict. Several models have been used as tools to estimate losses and to identify variables that will impact the rate and magnitude of loss. Considering the broad range in soil properties and climatic conditions used, some models performed well. However, modeling results and predictions are only estimates, and the fate and transport of triazines in the soil environment has been shown to be affected by many factors, including concentration, soil texture, variation in climate, and differences in tillage practices.