An analysis was made of the transport and fate of the organophosphate pesticide chlorpyrifos in productive soils from the Alto Valle of the Río Negro in Argentine Patagonia. The climate of the region is arid, so traditional fruit production is under flood irrigation. The soils in the floodplain are predominantly Aridisols with textures ranging from sandy loam to clay loam. The calibration was performed with water table data and chlorpyrifos concentration in the soil horizons. Field experiments made with Brilliant Blue FCF at the profile scale enabled the parametrisation of the dual-permeability model MACRO. The model calibration was evaluated by a comparison of observed and simulated data and statistics. The simulation of the groundwater table depth was satisfactory and the chlorpyrifos leaching revealed a different pattern in the two soil types studied. The sandy loam texture soil produced more percolation of irrigation water, but the clay loam soil produced greater leaching of chlorpyrifos under similar application conditions, presumably due to preferential flow under non-equilibrium conditions. Productive management alternatives to reduce leaching into the underlying unconfined aquifer were simulated. Among these, the incorporation of organic matter was the best alternative.
Keywords: MACRO model; Macropore; Organophosphate; Pesticide; Solute transport; Water quality.
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