Predicting the off-site deposition of spray drift from horticultural spraying through porous barriers on soil and plant surfaces

Abstract

Shelterbelts can be used to capture spray drift from crop spraying and reduce its spread to non crop areas. Critical factors in the efficiency of this capture are the ambient wind velocity, the structure of the shelterbelt and the spray drift droplet distribution. Here we present a model of the flow through and over a shelterbelt. It is found that the flow pattern is largely independent of the ambient wind strength. Settling and evaporation of the spray drift droplets are investigated and critical droplet diameters determined. It is found that droplets larger than 200 microns settle before reaching the shelterbelt and need not be included in the shelterbelt capture calculations. A model of the spray drift collection within the shelterbelt is analysed. Wind speeds between 1 and 5 m/s are considered which is the range that spray operations are usually performed over. Shelterbelts with optical porosities between 10% and 30% and constructed of fine particles such as pine needles are found to perform the best.