Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2006
Publication Date: 2/1/2007
Citation: Zablotowicz, R.M., Krutz, L.J., Reddy, K.N., Weaver, M.A., Koger III, C.H., Locke, M.A. 2007. Rapid development of enhanced atrazine degradation in a dundee silt loam soil under continuous corn and in rotation with cotton. Journal of Agricultural and Food Chemistry, Vol. 55, Number 3, pp. 852-859. Interpretive Summary: Use of a cotton corn rotation may have several economic and agronomic benefits to Mississippi Delta growers. The effect of a corn-cotton rotation compared to continuous corn or cotton was assessed on the potential for atrazine degradation and soil chemical and biological properties. Within a year of use of atrazine the potential for accelerated atrazine developed, and occurred nearly as rapidly in a corn and cotton rotation. Greater organic matter and nitrogen accumulated under continuous corn or a corn-cotton rotation compared to continuous cotton, and microbial communities were also affected by these cropping systems. Bacterial strains capable of complete degradation of atrazine to inorganic components were isolated from these plots, demonstrating the biological basis for accelerated atrazine degradation. Accelerated degradation may mean less pesticide is available for contamination of water resources, however, there may be a corresponding loss of weed control efficacy. New studies have been initiated to ascertain the effect of accelerated atrazine degradation on weed control potential.
Technical Abstract: Mississippi Delta cotton production in rotation with corn was evaluated in field experiments during 2000 to 2005 at Stoneville, MS. Plots maintained under minimum tillage were established in 2000 on a Dundee silt loam soil with treatments including continuous cotton or corn and alternate cotton corn rotations. Mineralization and dissipation of 14**C [ring]-labeled atrazine was evaluated in the laboratory on soils collected prior to herbicide application in the first, second, third and sixth year of the study. In soils collected in 2000, a low rate of atrazine mineralization was observed, 10% at 30 d. After one year of herbicide application, atrazine-treated soils mineralized 52 to 57% of the radio-labeled atrazine in 30 d. By the sixth year of the study, greater than 59% of the atrazine was mineralized after 7 d in soils treated with atrazine, while soils from plots with no atrazine treatment mineralized less than 36%. The data also indicated rapid development of enhanced atrazine degradation in soils following one year of corn cultivation with atrazine use. Atrazine mineralization was generally as rapid in soils under a rotation receiving biannual atrazine applications as in soils under continuous corn receiving annual applications of atrazine. Cumulative mineralization and mineralization kinetics parameters derived from the Gompertz model (K and Ti) were highly correlated with history of atrazine application and total soil carbon content. Changes in the soil microbial community assessed by total fatty acid methyl ester (FAME) analysis indicated significant interactions of cropping system and sampling date, with FAME indicators for soil bacteria responsible for differences in community structure. Pure cultures of atrazine-mineralizing bacteria were isolated from these plots confirming the biological basis for atrazine mineralization. These results indicate that changes in degradative potential of a soil can occur rapidly and some changes in soil properties may be associated with cropping systems can contribute to enhanced atrazine degradation potential.