|Smith jr, Sammie|
Submitted to: Bulletin of Environmental Contamination and Toxicology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/29/2005
Publication Date: 10/4/2005
Citation: Cerdeira, A.L., Domelas-Desouza, M., Bolonhesi, D., Queiroz, S.C., Ferracini, V.L., Ligo, M.A., Pessoa, M.C., Smith Jr, S. 2005. Effects of sugar cane mechanical harvesting followed by no-tillage crop systems on leaching of triazine herbicides in brazil. Bulletin of Environmental Contamination and Toxicology. (2005) 75:805-812 Interpretive Summary: In southern Brazil there is concern about herbicides leaching to shallow water tables in agricultural fields where sugarcane and peanuts are often grown in rotation. Therefore, field and laboratory studies were conducted to determine the effects of no-till (NT) and conventional-till (CT) on soil properties and potentially on leaching of certain herbicides to the underlying aquifer. Certain soil properties appeared to be affected by tillage, but not others. Tillage, however, did not seem to generally affect herbicide leaching. Further studies will be conducted in order to understand better the effects of those soil tillage systems and consequent impact on ground water quality. This research emphasizes the need to thoroughly study soil properties and agricultural field preparation systems in aquifer recharge areas with shallow water tables where agricultural production with relatively water soluble herbicides has the potential to result in herbicide leaching to the water table and thus contaminate the aquifer.
Technical Abstract: Both a field experiment and a soil column leaching study were conducted to determine the movement of triazines where mechanical sugarcane harvesting has been followed by no-till (NT) and conventional-till (CT) peanuts production. Although not all the triazines are necessarily used at same level on all crops, we have used the three, atrazine, simazine and ametryn as models to study the effect of soil preparation systems on selected soil properties and herbicide leaching in these soils. Our results have shown a general trend of higher density in soils under NT, mainly at the top layer. Our data have also shown no effect on microporosity, macroporosity, and total porosity when under the CT or NT systems. Some authors found reduction in runoff and increasing in leaching of atrazine and simazine in NT as opposed to CT, which is contradictory to our findings. Others have found the opposite, NT runoff was higher and leaching was lower, results similar to those found in our study. There were also great differences in literature regarding the tillage effects on hydraulic conductivity. In our study, there was a higher conductivity for soils submitted to CT than NT but this did not reflect on the movement of the triazines. The soil columns studies have shown the leaching of the herbicides atrazine and simazine down to the maximum of 20 cm. No herbicide was detected under 20 cm for the conditions of the experiment indicating less mobility under the experimental conditions than in mathematical modeling simulations. Ametryn was not detected in any depths. Atrazine and simazine were just found at the top layer from zero to 20cm in the soil columns studies. In both systems NT and CT, atrazine has leached more than simazine, what was expected according to studies conducted with mathematical simulation. There was no clear difference on mobility of both herbicides due to the tillage systems.