Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/1998
Publication Date: N/A
Citation: Interpretive Summary: Sorption is one of the most important processes impacting pesticide fate under field conditions, as it retards the movement of chemicals through the soil profile. The intensity and extent of retardation depends upon soil physical and chemical properties such as particle size and soil organic matter content, however, these properties can vary spatially and temporally yin the field. Our objectives were to determine the spatial variability of sorption parameters of imazethapyr, a herbicide widely used in soybean in US, in a field site and to relate sorption to easily determined soil properties. Simple screening models based on soil properties available from routine soil tests or regional soil surveys could then be developed to identify areas where herbicide sorption would be minimal and the potential for leaching the greatest. Under precision agriculture concepts, this might lead to the implementation of site-specific management of herbicide usage. The analysis of sorption values showed two distinct patterns in spatial distribution (below and above pH 6.25), and this was used as criteria to divide the field into two potential management areas, for applying site-specific treatments. The decision about eventual rates to be applied, however, will depend on a more complex analysis, which might include the level of weed infestation and distribution, availability of adequate spraying equipment, and economic analysis. As a result of this research, the farmer will be able to reduce herbicide use and reduce the risk of potential adverse environmental impact for the herbicide that is used.
Technical Abstract: A significant limitation of use of sorption coefficients (Kd) to predict solute transport through natural soils is the spatial variability of soil properties over large field areas. Spatial variability in Kd was determined on representative samples from a 31.4-ha field, covering a pH range from 4.9 to 7.6 and an OC range from 1.45 to 5.80 g kg**-1. Kd varied from 0.18 to 3.78 across the field, with an average value of 1.56. The analysis of Kd variability showed two distinct patterns in spatial distribution: areas in which pH greater than 6.25 and Kd less than 1.5, where Kd variation is based primarily on pH variation; and areas in which pH less than 6.25 and Kd greater than 1.5, where other soil properties, such as texture and OC content have a significant influence on Kd variation. Based on soil pH distribution, an easily measured property, the field was divided in two potential management areas. This separation allowed identification of portions of the field where herbicide sorption would be minimal, with a relatively higher potential for leaching (i.e. areas with Kd less than 1.5), and provided a background to evaluate the possibility of applying site-specific imazethapyr treatments.