Submitted to: American Society for Testing and Materials
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2005
Publication Date: 1/1/2006
Citation: Hoffmann, W.C. 2006. Field-collected and AGDISP-predicted spray flux from an aerial application. Journal of ASTM International. 3:doi:10.1520/JAI12908. Interpretive Summary: Computer models are increasingly being used by regulators, aerial applicators, and researchers to understand and predict the impacts of weather, application equipment, and other factors on the deposition and movement of applied crop protection materials within and around the intended target site. This study compared field or 'real world' data obtained in soybean and cotton canopies with the predicted data from a commonly-used computer model called AGDISP. There was generally very close agreement between the field data and the model predicted data. This study will increase the confidence that AGDISP users have in the model and aid in validating the model.
Technical Abstract: As computer models are increasingly being integrated into modern 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 was 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. There were good correlations between the spray flux or amount of material moving downwind from an aerial application as measured by samplers in the field and the spray flux predicted by the AGDISP model. Surface roughness coefficients over bare ground had minimal impacts. A 1.5 m/sec increase in wind speed resulted in a 100 percent increase in the spray flux at 50 m from the application site. When crop height 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.