ARS | Publication request: SPATIAL AND TEMPORAL VARIABILITY OF AGRICULTURAL CHEMICALS AT FIELD AND WATERSHED SCALES

Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2003
Publication Date: June 15, 2003
Citation: Graff, C.D., Rice, C., Sadeghi, A.M. 2003. Spatial and temporal variability of agricultural chemicals at field and watershed scales [abstract]. BARC Poster Day. June 2003.

Technical Abstract: Soil and landscape characteristics that influence herbicide behavior through soil/sorption, dissipation, and transport processes vary spatially at the scales of most agricultural fields. Knowledge of the spatial variability in herbicide dissipation could lead to site-specific management practices to reduce off-site transport while maintaining viable weed control. Experiments on a 6 ha watershed were conducted in order to characterize the spatial variability of acetochlor and isoxaflutole behavior. Spatial distribution of surface soil properties was determined for the watershed. Terrain attributes were derived from a Digital Elevation Model in order to ascertain if they could enhance the prediction of acetochlor and isoxaflutole behavior. Acetochlor and isoxaflutole were applied at uniform recommended rates in 2000 and in 2001. At various times, soil samples were taken to a depth of 70 cm at numerous georeferenced locations having a range in soil properties representative of the site. It was found that acetochlor dissipation was rapid and varied across the field. Isoxaflutole degradation to diketonitrile (DKN) was also rapid and variable across the field; however, DKN did not rapidly degrade between sampling times. Geostatisical analysis revealed that acetochlor and DKN dissipation rates exhibit spatial structure. The temporal spacing in the sampling events was not adequate to capture the spatial dependency of the rapid isoxaflutole dissipation. The relationships between acetochlor dissipation and soil/terrain attributes were found to be complex and varied between sampling times and years. The techniques described above could potentially be modified in order to understand dissipation at the watershed scale. Characterizing the spatial variability of surface and subsurface herbicide dissipation in a first-order agricultural watershed with a riparian buffer zone will be discussed.