Role of Atmospheric Stability in Drift and Deposition of Aerially Applied Sprays - Preliminary Results

Abstract

Drift from aerial application of crop protection materials is influenced by many factors,including atmospheric stability. The applicator is responsible for insuring that all factors areconsidered and that all possible efforts are made to reduce the potential for drift. Atmosphericconditions must be considered and adjustments made based on real time observations and pastexperience. Many studies have indicated that a more stable atmosphere increases the potential fordrift. It is therefore important to have an understanding of atmospheric stability and how it canimpact the deposition and drift of aerially applied sprays. The objective of this research was todocument the effects of atmospheric stability, especially under very stable to stable conditions, onthe deposition and drift of aerially applied sprays. Two treatments, a FINE and a MEDIUM spray,were used. Ground deposition and airborne concentrations of spray were sampled at multipledownwind locations using mylar cards and monofilament line, respectively. Tests were performedbeginning at first light and continued for approximately two hours. Sampling during these times gavea high probability that stable and very stable conditions would be encountered.<br><br>Statistical and graphical analyses indicated that there were no significant differences betweentreatments, but that stability had a significant effect on ground deposition in the near-field and onairborne concentrations in the far-field. Regression analysis indicated that wind speed was asignificant factor for both ground deposition and airborne concentrations in both the near-field andthe far-field. These results tend to support previous findings. Several difficulties that turned up in the analysis are discussed, including lack of sufficient samples during stable and very stable conditionsand a need for additional sampling heights. Solutions being implemented in the next set of fieldstudies, i.e. additional sampling heights at each downwind distance location and methodology toincrease the number of replications, are also discussed.