|Lin, C - UNIVERSITY OF MISSOURI|
|Garrett, H - UNIVERSITY OF MISSOURI|
|Jordan, J - ALABAMA STATE UNIVERSITY|
|George, M - UNIVERSITY OF MISSOURI|
Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 12, 2006
Publication Date: May 14, 2007
Citation: Lin, C.H., Lerch, R.N., Garrett, H.E., Jordan, J., George, M.F. 2007. Ability of forage grasses exposed to atrazine and isoxaflutole (Balance) to reduce nutrient levels in soils and shallow groundwater. Communications in Soil Science and Plant Analysis. 38:1119-1136. Interpretive Summary: Successful vegetative buffers need grass species that can capture nutrients before they run off the surface or leach to groundwater. A field study at the University of Missouri’s Horticulture and Agroforestry Center using five grass treatments (orchardgrass, tall fescue, smooth bromegrass, timothy, and switchgrass) plus a bare ground control treatment evaluated the ability of the grasses to scrub nutrients from soils and shallow groundwater. All treatments received equal amounts of nitrate (NO3-) and phosphate (PO43-). In addition, half of the treatments received either atrazine or isoxaflutole (BalanceTM) at levels typically in surface runoff from cropland to see if the herbicides would slow the grass growth. Timothy reduced nitrate levels in leachate by 75% compared to the control; the other grasses were all much better, reducing nitrate leaching by ~99% compared to the bare ground control. In addition, grass treatments reduced soil nitrate levels by 41 to 91% below the control. Denitrification, or the conversion of nitrate to gaseous nitrogen forms, was apparently greatest in switchgrass, smooth bromegrass, and tall fescue treatments. Switchgrass also reduced phosphate leaching by 60 to 74% compared to the control. The ability of the forage grasses to reduce nutrient levels in soil or shallow groundwater was not significantly affected by either herbicide. Overall, switchgrass, smooth bromegrass, and tall fescue are the most suitable for use in vegetative buffers because of their superior ability to reduce soil nitrate and nutrient leaching. Farmers, extension personnel, state conservation agencies, and USDA-Natural Resource Conservation Service will benefit from this work. These results can be used to design better grass buffer systems that will effectively reduce contamination of surface and ground waters by nutrients used in row-crop production.
Technical Abstract: Successful implementation of vegetative buffers requires inclusion of plant species that facilitate rapid dissipation of deposited contaminants before they have a chance to be transported in surface runoff or to shallow groundwater. Thirty-six field lysimeters with six different ground covers [bare ground, orchardgrass (Dactylis glomerata L.), tall fescue (Festuca arundinacea Schreb.), smooth bromegrass (Bromus inermis Leyss.), timothy (Phleum pratense L.), and switchgrass (Panicum virgatum L.)] were established to evaluate their ability to reduce nutrient levels in soils and shallow groundwater. Nitrate (NO3-) and ortho-phosphate (PO43-) were uniformly applied to each lysimeter. In addition, half of the lysimeters received an application of atrazine and the other half received isoxaflutole (BalanceTM) at levels indicative of surface runoff from cropland. The leachate from each lysimeter was collected after major rainfall events during a 25-day period and soil was collected from each lysimeter at the end of the 25-day period. Water samples were analyzed for NO3-N and PO4-P and soils were extracted and analyzed for NO3-N. Grass treatments reduced NO3-N levels in leachate by 74.5 to 99.7% compared to the bare ground control, but timothy was significantly less effective at reducing NO3-N leaching than the other grasses. Grass treatments reduced residual soil NO3-N levels by 40.9 to 91.2% compared to the control, with tall fescue, smooth bromegrass, and switchgrass having the lowest levels. Switchgrass decreased PO4-P leaching to the greatest extent, reducing it by 60.0 to 74.2% compared to the control. The ability of the forage grasses to reduce nutrient levels in soil or shallow groundwater were not significantly affected by herbicide treatment. Quantification of microbial NO3 dissipation rates in soil suggested that denitrification was greatest in switchgrass, smooth bromegrass, and tall fescue treatments. The overall performance of these three grasses indicated that they are the most suitable for use in vegetative buffers because of their superior ability to dissipate soil NO3- and reduce nutrient transport to shallow groundwater.