AGDISP Sensitivity to Crop Canopy Characterization

Authors: Hoffmann, Wesley; Fritz, Bradley - Brad; Martin, Daniel - Dan

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/1/2007
Publication Date: 7/18/2007
Citation: Hoffmann, W.C., Fritz, B.K., Martin, D.E. 2007. AGDISP sensitivity to crop canopy characterization. Transactions of the ASABE. 50:1117-1122.

Interpretive Summary: AgDISP is a computer model that is 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 aerial spray deposition and movement measurements in six cotton canopies to predicted data from the AgDISP model. There was generally very close agreement between the field data and the model predicted data in canopies from 0.3 to 0.8 m tall; however, there were differences between measured and predicted data for aerial applications over bare ground and very dense canopies. This study will increase user confidence in the AGDISP model and aid in validating the model.

Technical Abstract: As computer-based decision and modeling systems become increasingly integrated into American agriculture, it is important that users of these systems have the understanding of the effects that various inputs have on systems. The objective of the work presented is to quantify the effects that different crop canopy characteristics, such as height and canopy closure, have on aerially-applied spray deposition and downwind movement and compare these results to the predictions of spray movement and deposition by the AgDISP, a computer model. Six trials were conducted in cotton fields ranging from bare ground up to 1 m in height and canopy closure ranging for 0-100%. Horizontal deposition measurements were used to verify that each of applications made during each of the trials produced similar levels of deposition. Monofilament string were placed at four sampling heights (1, 2 ,4 and 6 m) above the canopy at a distance of 50 m from the downwind edge of the spray swath to measure the airborne droplets at this distance. The vertical deposition values at 50 m for crop heights between 0.3 and 0.8 m were comparable between the field collected and AgDISP predicted data. The AgDISP model overpredicted by a factor of 2 the levels of spray at 1 m for the trials conducted at 0 or 1 m crop canopy height as compared to field measurements; however, at 4 and 6 m above the ground, the AgDISP and field data were very comparable. Users of the AgDISP should be encouraged by the accuracy of the model but are cautioned when using the model with canopies that are closed more than 80%.