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As computer models are increasingly being integrated into modem agricultural operations, the comparison of field-collected data to the model prediction improves the confidence that aerial applicators, researchers, and regulators have in the model. The field-collected data were compared to the AGDISP model predictions for the tests conducted in soybeans and cotton and over a concrete runway on two different days. The meteorological effects on spray movement were then explored by analyzing individual replications in the spray trials. The effect of varying the surface roughness coefficient over the range of values for bare ground (i.e., runways) in the AGDISP model on downwind spray movement was determined. The final analyses presented showed the dramatic decrease in downwind spray movement as a result of increasing canopy height as predicted by the AGDISP model.
The AGDISP model predicted 1–6 times higher levels of spray materials than that measured by field samplers. The model predictions were 1–3 times greater than the field collected data in the runway studies and 2–6 times greater in the canopy studies. Surface roughness coefficients over bare ground had minimal impacts as predicted by the AGDISP model. When the actual weather conditions of one of the treatments in this study were input into the AGDISP model, a 1.5 m/s increase in wind speed resulted in a 100 % increase in the spray flux at 50 m from the application site. When crop height inputs into the AGDISP model were changed from 0.3 m to 1.3 m, the spray flux decreased by 20-fold, demonstrating the dramatic filtering effect that a canopy can have on a spray cloud and will serve as a stimulus for future studies designed to fully characterize the effect of crop canopy on spray movement.
spray deposition, drift, AGDISP, aerial application, canopy
Agricultural Engineer, USDA-ARS-Areawide Pest Management Unit, College Station, TX