ABSTRACT
D.E. CRUCIANI, G C. BAPTISTA, P.J. CHRISTOFFOLETI and K. MINAMI Escola Superior de Agricultura "Luiz de Queiroz", University of Sao Paulo, Brazil
Abstract The fate of soil herbicides and their impact on the environment plays an important role in the assessment of the agricultural efficiency of these chemicals. Soil drainage may influence movement, infiltration and mobility through the soil profile and, consequently their presence in the groundwater. Therefore, the purpose of this research was to ascertain the effect of a soil drainage system on the surface and lateral movement, leaching and groundwater contamination by the herbicide trifluralin sprayed on corn crop in pre-emergence conditions. The experiment was conducted from January to April of 1995 at the drainage experimental field of the Department of Rural Engineering, ESALQ/USP. Surface removal of herbicides by run-off in the well drained blocks was found to be much less compared to the check block (no drainage). Herbicide infiltration in the soil was found to be directly related to drainage as indicated by a retention four times higher in drainage blocks than in the no-drainage block. Herbicide residues in drainage water were insignificant considering that the water table was at an average depth of 0.60 cm below surface. Residuals found on the soil surface, in the 0-15 cm soil layer and in groundwater allowed for the conclusion that subsurface drainage reduces movement and leaching of the herbicide and thus the risks of environmental contamination. Keywords: Drainage, environmental impacts, herbicide, leaching, low-land areas, subsurface drainage.
