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Field study of pesticide leaching

Abstract

We applied 5 pesticides, along with bromide as a conservative tracer, at 2 field sites (Northland and Manawatu, North Island of New Zealand), and their distributions in the soil profile were monitored through soil core and suction cup sampling for 18 months. Field-measured values were simulated using LEACHM, HYDRUS-1D, GLEAMS, and SPASMO models and compared against the measured datasets at both these sites. All 4 models predicted the measured dataset for each of the compounds with reasonable degree of accuracy; however, some discrepancies were observed. Prediction by GLEAMS was by far the best, as indicated by the goodness of fit parameters. Pesticide leaching parameters, organic carbon partition coefficient (Koc), and degradation half-life (T1/2) were optimised using the PEST optimisation package. For diazinon and terbuthylazine the parameters obtained for each of the models were generally close to the literature range. However, Koc and T1/2 values for atrazine, hexazinone, and procymidone were found to be slightly lower than the available literature range data.

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