The Effect of Boom Section and Nozzle Configuration on the Risk of Spray Drift

The effect of spray characteristics and boom section on spray drift produced by agricultural flatfan nozzles has been investigated using wind-tunnel techniques. Variations in the effective spray plume porosity to an air stream were achieved by varying spray quality and varying nozzle spacing from 125 to 750 mm, in six steps. Three boom sections were used: a standard boom; a deep boom, for maximum air stream blockage, and a profile boom for reduced vertical dispersion. Wind speeds were varied from 1·0 and 3·0 m/s. Flow visualization techniques showed that the air stream pattern varied with plume porosity and mean air velocity. Measurements of airborne spray, 2 m downwind of the nozzles, showed that drift decreased as sprays changed in quality from fine to coarse using British Crop Protection Council scheme as expected. Maximum airborne drift occurred at a nozzle spacing of 500 mm with all spray qualities. Although the vertical profile of airborne drift was influenced by boom section, the magnitudes of difference between extremes of boom configuration were much less than changes due to nozzle characteristics. Variations in drift risk are characterized by the mean drift, mean drift moment and section moment, and could provide a mechanism for the assessment of various boom shapes and designs in combination with different nozzle conditions.