Submitted to: Cotton Research and Extension Report
Publication Type: Experiment Station
Publication Acceptance Date: March 20, 2001
Publication Date: March 20, 2001
Citation: POTTER, T.L., HUBBARD, R.K., BEDNARZ, C., GATES, R.N., HANNA, W.W. USE OF GRASS FILTER STRIPS TO REMOVE DEFOLIANT RESIDUES IN RUNOFF FROM LAND IN COTTON PRODUCTION. 2000 COTTON RESEARCH AND EXTENSION PUBLICATION #4. PP. 184-193. 2001. Interpretive Summary: Effective and efficient conservation buffer use to control non-point source pollution from cropland runoff requires that design features be systematically evaluated for factors like crop type and climatic and soil conditions. To this end, research is needed on the Coastal Plain where cotton acreage has more than doubled in the past decade. Of particular concern are residues of the chemicals used to defoliate prior to picking. Studies conducted in Tift County Georgia showed that up to 15 % of the active ingredients contained in the two most widely used defoliants may be carried from fields in runoff. This observation lead to our investigation of the efficacy of grass filter strips installed at the edge of cotton fields to control potential impacts. Two grass types and two filter lengths were included in the experimental design. In crop-year 2000, some promising results were obtained. The levels of defoliants in runoff following four post-application rain storms were reduced by 5 to 36 times when the concentrations of residues in samples collected at the edge of the cotton fields were compared to concentrations of samples collected in the middle and the end of the grass-filters. These results should be of interest to all stakeholders in the cotton industry and Coastal Plain agriculture. This includes growers, conservationists, state and federal land managers, and regulators. Our studies have demonstrated that grass filters may be an effective way of minimizing environmental impacts of cotton production.
Technical Abstract: Eighteen 0.1-acre plots were established on a sloping field in Tift County Georgia. The soil is a Tifton loamy sand with 2.0 to 3.0 % slope. Plots were subdivided at their mid-points on the lengthwise dimension. Cotton was planted on the upper half of each plot on May-2000. The lower half of 9 plots was sprigged with common Bermuda grass (Cynadon dactylon L. Pers.) and 9 with "Tifton 85" Bermuda grass. Runoff collectors were installed at the bottom edge of the cotton and at the mid-point and bottom edge of the grass filters on 3 plots of each grass type. Two weeks prior to machine picking on September 28, 2000, a tank mixture containing two commercial defoliant products, DEF and Dropp, was applied. Active ingredients were tribufos and thidiazuron. Runoff samples were collected following four storm events during the three-week period after defoliant application. Relatively high levels of both compounds, 8 to 30 ug L-1 were detected in edge-of-cotton-field samples following the first two post-application stor events. Concentrations in corresponding samples collected at the mid-point and at the lower edge of the grass filters was 5 to 36 times lower. Results have indicated that grass filters can significantly reduce tribufos and thidiazuron concentrations in runoff and that they may be an effective means of limiting environmental impacts of cotton production.