|Lin, C - U OF MO|
|Garrett, H - U OF MO|
|George, M - U OF MO|
Submitted to: North American Agroforestry Conference
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2003
Publication Date: N/A
Technical Abstract: A lysimeter study with six different ground covers (bare ground, orchardgrass, tall fescue, timothy, smooth bromegrass, and switchgrass) was established to evaluate the effect of forages on atrazine (ATR) and Balance (isoxaflutole) fate. Each lysimeter received either 1500 ug of atrazine or 240 ug of isoxaflutole. Soil and above ground plant tissue were sampled 25 days following herbicide application. Concentrations of ATR, Balance, and their metabolites in soil and plant tissues were determined by solid phase or liquid-liquid extraction followed by either GC/MS/MS or HPLC/MS/MS analyses. The results suggested that forage treated lysimeters, especially those with switchgrass, significantly enhanced the degradation of ATR in the soil through N-dealkylation and/or hydroxylation. Approximately 80.7% of atrazine in the soil was degraded into less toxic forms by switchgrass. Smooth bromegrass, timothy, orchardgrass, and tall fescue also showed significant capacity (66.5 to 74.7%) to degrade atrazine in the soil as compared to the control (55.5%). In contrast, the degradation of diketonitrile (DKN), the first degradation product and biologically active form of Balance, in soil appears to be an abiotic process. The results also indicated that the total uptake of Balance residues was strongly correlated with the transpiration rates of the forages. The capacity of forages to convert DKN to a nonphytotoxic benzoic acid metabolite was strongly associated with their tolerance to this new herbicide. In a bioremediation system utilizing the forages tested here, the enhanced biological degradation/immobilization by the forage will play an essential role in the removal of ATR. On the other hand, the abiotic nature of DKN degradation in the soil implies that physical trapping is likely to be the primary remediation mechanism for Balance removal.