|Leonard, Ralph - ARS (RETIRED)|
Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 2000
Publication Date: December 1, 2000
Citation: BOSCH, D.D., TRUMAN, C.C., LEONARD, R.A. ATRAZINE AND CARBOFURAN TRANSPORT THROUGH THE VADOSE ZONE IN THE CLAIBORNE AQUIFER RECHARGE AREA. TRANSACTIONS OF THE AMERICAN SOCIETY OF AGRICULTURAL ENGINEERS. 43(6):1609-1620. 2000. Interpretive Summary: Losses of agricultural chemicals from the area of the soil containing the plant roots are important relative to both crop production and environmental quality. When these chemicals leave the root zone they are no longer available for crop protection and growth and may negatively impact surface or subsurface water quality. The movement in the soil and decay rate of the agricultural herbicide atrazine, two of the compounds formed as atrazine decays, and the insecticide carbofuran were measured. Overall, the higher concentrations of the chemicals were limited to the top 25 cm of the soil and to the period from 1-30 days after the pesticides were applied. On the average, by 30 days after application of the pesticides 83% of the atrazine and 96% of the carbofuran had degraded. Despite the sandy nature of the soils studied, the amount of the pesticides transported to deeper in the soil profile was small. The high temperatures and adequate moisture conditions contributed to rapid decay of the studied chemicals. This study will help scientists and land managers design better methods for preventing environmental problems due to agricultural practices.
Technical Abstract: A 1 ha field plot with a sandy surface soil, located near Plains, Georgia, was studied for three years (1993-1995) to evaluate pesticide transport in the vadose zone. Vadose zone soil samples collected prior to corn planting and pesticide applications, at approximately 1, 3, 7, 14, 28, and 44 days after pesticide application (DAPA), each fall, and in the spring of f1995 prior to planting were analyzed for atrazine, carbofuran, deethyl- atrazine (DEA) and deisopropylatrazine (DIA). Atrazine and carbofuran in the active root zone degraded rapidly. Overall, the higher concentration levels of atrazine and its metabolites and of carbofuran were limited to the top 25 cm of the profile and to the period from 1 to 30 DAPA. On the average, by 30 DAPA 83% of the atrazine and 96% of the carbofuran had degraded. Atrazine was found to be more persistent than was carbofuran with a half life approximately twice that for carbofuran. A two-stage model with ha variable dissipation rate for the period up to 44 DAPA and a second dissipation rate for periods greater than that was found to fit the data better than a single stage model. For the first 44 DAPA, the first order decay rate with a half life of 12 days was found to fit the field data quite well for atrazine within the soil profile. A first order decay rate with a half life of approximately 6 days fit the observed carbofuran data best. When a two stage dissipation process was assumed, the dissipation rate coefficient decreased from 0.059 to 0.006 (days**-1) for atrazine, while for carbofuran it decreased from 0.110 to 0.018 (days**-1).