|Lerch, Robert - Bob|
Submitted to: North American Agroforestry Conference
Publication Type: Proceedings
Publication Acceptance Date: 4/16/2005
Publication Date: 6/30/2005
Citation: Lin, C.H., Lerch, R.N., Kremer, R.J., Garrett, H.E., Udawatta, R.P., George, M.F. 2005. Soil microbiological activities in vegetative buffer strips and their association with herbicide degradation. North American Agroforestry Conference. Available: http://cinram.umn.edu/afta2005/. Interpretive Summary: Grass buffer systems can reduce the impact of non-point source pollution by slowing runoff velocity and trapping sediment, nutrients, and herbicides. A sound buffer design should also promote rapid breakdown of deposited herbicides so that they are not later released to surface and subsurface flow. We studied how vegetative buffers affected soil microbial enzyme activities and herbicide degradation. A field study was conducted on three small watersheds with different land uses: contour grass buffers with row crops; contour tree-grass agroforestry buffers with row crops; and row-crop only as a control. The results from the field watersheds showed that enzyme activities were higher in grass and tree-grass buffers than in the cropped control treatment. Among the watersheds, soils collected from the grass buffers showed the highest enzyme activities and herbicide degradation potential at all landscape positions. A growth chamber study showed that two of the three enzymes measured were good predictors of atrazine degradation. Therefore, the results from the field watersheds strongly suggested that grass and tree-grass buffers will enhance the degradation of herbicides. Corn growers, extension personnel, state conservation agencies, and USDA-Natural Resource Conservation Service will benefit from this work since these results indicated that vegetative buffers can enhance herbicide degradation, and it further illustrates the potential benefits of incorporating vegetative buffers into cropping systems to effectively reduce herbicide contamination associated with crop production.
Technical Abstract: The efficacy of vegetative buffer strips in intercepting herbicides from surface runoff is well established. A sound buffer design should also facilitate rapid degradation of deposited herbicides before they have a chance to be released to surface and subsurface flow. Experimental plots were arranged in a split-plot design with three replications and a factorial combination of three land use treatments with five landscape positions (summit, shoulder slope, back slope, foot slope, and toe slope). Land use treatments included a contour grass buffer watershed, a contour tree-grass agroforestry buffer watershed, and a control watershed. Watershed areas ranged from 1.65 to 4.44 ha. All land-use treatments were in a corn-soybean minimum-till production system, and the vegetative buffers were contoured strips from the summit to toeslope positions. To evaluate microbial activities and herbicide degradation potential, B-glucosidase, dehydrogenase and fluorescein diacetate hydrolytic activities were measured. The results suggested that the microbial enzymatic activities were significantly higher in grass and tree-grass buffers than in the control treatment. Among the treatments, the soils collected from the grass buffers showed the highest microbial enzymatic activities and herbicide degradation potential. Topographic position did not significantly affect soil microbial activities. A growth chamber study was also conducted to investigate the microbial mineralization rates of 14C ring labeled atrazine and the activities of FDA, dehydrogenase and B-glucosidase in the rhizosphere of seven selected forages treatments. Preliminary results suggested that the mineralization rates of atrazine, after 100 days of incubation, were more closely correlated with activities of B-glucosidase (r = 0.857) and dehydrogenase (r = 0.763) than FDA hydrolysis rates (r = 0.494). Efforts are currently under way to correlate the microbial activity in different land use treatments with herbicide mineralization and degradation rates using 14C-labeled herbicides, such as atrazine, bentazon, pendimethalin, s-metolachlor and glyphosate.