|Lerch, Robert - Bob|
Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/8/2003
Publication Date: 1/20/2004
Citation: Lin, C.Y., Lerch, R.N., Garrett, H.E., George, M.F. 2004. Incorporating forage grasses in riparian buffers for bioremediation of atrazine, isoxaflutole and nitrate in Missouri. Agroforestry Systems. 63:91-99. Interpretive Summary: Grass buffer systems can reduce the impact of non-point source pollution by slowing runoff velocity, trapping sediment, promoting pesticide degrada- tion, and removing nutrients by direct uptake. However, many factors must be considered in the choice of the most appropriate grass species for use in buffer systems that also include shrubs and trees, such as those established in riparian areas. High herbicide concentrations in runoff water and shade from trees can reduce the effectiveness of grasses in these riparian buffer systems. The main objective of this study was to evaluate several forage grass species for their suitability in riparian buffer systems based on their shade and herbicide tolerance and ability to remove nitrate from contaminated water. Greenhouse and field studies were conducted to evaluate the potential use of orchard grass, smooth bromegrass, tall fescue, timothy, and switchgrass in buffer systems. Herbicide tolerance was evaluated for atrazine and Balance (isoxaflutole), a recently released corn herbicide. Based on these studies, switchgrass, tall fescue, and smooth bromegrass showed the most potential for use in tree-shrub-grass riparian buffer systems. These species provide the best overall ability to remediate contaminated water while maintaining their vigor under partially-shaded conditions. Corn growers, extension personnel, state conservation agencies, and USDA-Natural Resource Conservation Service personnel will benefit from this work because these results can be used to better design grass and riparian buffer systems that will effectively reduce herbicide and nutrient non-point source contamination associated with corn production.
Technical Abstract: Multi-species tree-shrub-grass riparian buffer systems have been recognized as one of the most cost-effective bioremediation approaches to alleviate non-point source agricultural pollution. However, highly concentrated herbicides in surface and subsurface water and shade cast by trees along the stream bank usually compromise the effectiveness of these systems. Greenhouse trials and field lysimeter studies were conducted to evaluate the tolerance of orchard grass, smooth bromegrass, tall fescue, timothy, and switchgrass ground covers to atrazine and Balance plus their capacity to sequester and degrade these herbicides and their metabolites. Removal of soil nitrate was also quantified. Concentrations of atrazine, Balance, and their metabolites in the leachate, soil, and plant samples were determined by solid phase extraction followed by high performance liquid or gas chromatographic analyses. Distribution of the herbicides and metabolites in nthe system was calculated using a mass balance approach. Herbicide bioremediation capacity of each lysimeter treatment was determined by the ratio of metabolites to parent herbicide + metabolites. Bioremediation of nitrate was quantified by comparing nitrate reduction rates in grass treatments to the bare ground control. Based on herbicide tolerance, bioremediation data, and shade tolerance determined in a previous study, it was established that switchgrass, tall fescue, and smooth bromegrass are good candidates for incorporation in tree-shrub-grass riparian buffer systems designed for the bioremediation of atrazine, Balance, and nitrate.