Modelling to determine the optimal porosity of shelterbelts for the capture of agricultural spray drift

Shelterbelts are not only useful as windbreak protection for stock and crops but can also be used to capture spray drift and reduce the spread to non-crop areas with important environmental consequences. The porosity of a shelterbelt can significantly influence the ability to capture spray drift. The aim of this work is to determine the optimal shelterbelt porosity that maximises spray drift capture. This has implications to future shelterbelt plantings and species selection. Here a model is developed for the flow through and over a shelterbelt. This model is used in conjunction with a spray capture model to determine the capture efficiency of shelterbelts with different porosities. Values of the optical porosity between 10% and 40% are found to give the best capture efficiency over a range of shelterbelt structures with the optimum generally around 25%. It is hoped that in the future experimental validation of these models will be undertaken. This will further enhance the understanding and use of shelterbelts as spray mitigation devices.