EFFECT OF GROUND COVER, RAIN INTENSITY AND STRAWBERRY PLANTS ON SPLASH OF SIMULATED RAINDROPS

A study was conducted to characterize the general features of splash d roplets produced from impacting raindrops in an effort to better under stand rain splash dispersal of fungal plant pathogens. A rain generato r was used to produce simulated raindrops, with a distribution of drop sizes which was very similar to natural rain, that impacted on differ ent ground covers or strawberry plants through a 100-cm2 opening of a rain shelter. Three ground covers, i.e. soil, straw, and plastic mulch , were tested with simulated rains of 15 and 30 mm h-1 intensity. Effe ct of plant density was also evaluated by placing strawberry plants of different leaf area indices in the exposed area of the rain shelter. Water sensitive papers were used to collect splash droplets in order t o determine droplet size distribution, number and mass flux densities over distance from the raindrop impact area, and also mass reflection. The distribution of splash droplet size was found to be highly and po sitively skewed and was well fitted by the Weibull distribution functi on. The median size of splash droplets was less than 0.26 mm in diamet er, and the Weibull parameters were largely independent of rain intens ity. Both flux densities of splash droplet number and mass declined wi th distance from the window edge, and were represented by an exponenti al gradient model. The steepness of the gradients was found to increas e with surface roughness (i.e. steepest for straw, shallowest for plas tic), and decrease with rain intensity. Mass ratio of the splash dropl ets to the incident raindrops was in the range of 0.29 to 0.38 without the presence of strawberry plants, and was affected by ground cover, rain intensity, and their interaction. With raindrop impactions on pla nts, mass reflection was greatly reduced to 0.02-0.09. Results were co nsistent with, and help explain, the previously demonstrated relations hip between surface topography and splash dispersal of fungal spores.