Avaliação do risco de contaminação do lencol freatico, pelo herbicida tebuthiuron em cultura de cana-de-acucar, utilizando geoestatistica e simulador CMLS

AUTOR(ES)
DATA DE PUBLICAÇÃO

1999

RESUMO

Nowadays, sugar cane production demands application of several herbicides of which, tebuthiuron, has been largely used. In an area intensivelycropped with sugar cane and susceptible to leaching due to edaphic conditions, CMLS (ChemicalMovement in Layered Soils) model was used to evaluate ground water contamination risk with this herbicide. The main parametersrequired by CMLS model were measured of soil samples collected from an incomplete grid of regular sampling, with 111 equispaced sample points of 200m, delineated in Espraiado stream microbasin, situated between Ribeirão Preto and Serrana counties, São Paulo state, Brazil, 21°05 and 21°20 latitude South and 47°40 and 47°50 longitude W. Gr.. The following parameters were analyzed: buIk density (glcm3),organic carbon (%), field capacity (%), wilting point (%), and total porosity (%). CMLS was used to study the herbicide behavior, in Dusk Latosol (LR), Oxisols, Quartzous Sandy (AQ) and Dark Red Latosol soils, Entisols, with medium and clayey textures. The 373 point data evaluated by CMLS model were generated from the original grid samples, using geostatistical methods of variography and ordinary kriging applied to each variable and to each depth intervaloA map was traced to this set of point data, showing the herbicide behavior in terms ofdepth (m) reached, after six-year simulation (1989-1995). It was verified that, for Quartzous Sandy Soil (AQ), the herbicide tebuthiuron, in four simulated point data, showed depth values above 43m, with a maximumof SOm,and an amount of the product remained in the soil, almost 10% of the applied dose of 1.1kglha. These results are considered dangerous in relation to the contamination of ground water. For the other soils, DuskLatosol (LR) and Dark Red Latosol (LE), the contamination risk can be considered as inexistent for LR and from low to medium for LE, as the (soil) texture changes from clayey to medium, respectively. Results from the column experiment analysis used for the validation of the CMLS modeI, showed, with respect to the depth (em) reached by the herbicide, that result obtained by the model was overestimated in 6.66% the value produced by the column, for the Quartzous Sandy soil (AQ), Entisols, and under-estimated in 4.5% and 20.0%, for Dark Red Latosol (LE) and Dusk Latosol soils (LR), Oxisols, respectively. These data confirm the adequacy ofthe CMLS model, as a tool to evaluate fate of tebuthiuron to ground water, while are considered Quartzous Sandy (AQ) and Dark Red Latosol (LE) soils. As far as Dark Latosol (LE) is concemed, due to significant differences between model and laboratory experiment results, one cannot have the same conclusion

ASSUNTO(S)

herbicidas aguas subterraneas - contaminação modelos matematicos produtos quimicos agricolas pesticidas

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