INFLUENCE OF TARGET CHARACTERISTICS ON THE AMOUNT OF WATER SPLASHED BY IMPACTING DROPS

Experiments were done to investigate the influence of drop diameter on the efficiency of the splash process, using a rain tower and differen t types of target (glass, water films, healthy and/or diseased oilseed rape leaves and tobacco leaves) and different target configurations. For horizontal glass plates, random variability in the mass of water s plashed was 3-4 times greater for dry targets than for wet targets and considerably more water was splashed from wet targets. The effect of target angle was greater for large drops and the greatest amount of wa ter was splashed from horizontal targets. More water was splashed from oilseed rape leaves than tobacco leaves. Both spore suspensions and s urfactant in target liquids decreased the mean volume of water splashe d and increased its variability. A power law described the relationshi p between drop diameter and mass of water splashed per incident drop f or drops falling from a height of 11 m onto targets of different types . Using results obtained with incident drops falling from heights of 1 1 or 1.5 m there was no unique relationship between mass of water spla shed and kinetic energy, momentum or impact force. A simulation study, which calculated splash efficiency of single drops on leaves, illustr ated the importance of leaf characteristics when assessing rain-splash potential, and more generally when developing methodology to describe the influence of crop structure on the dispersal of spores by splash. (C) 1997 Elsevier Science B.V.