(A) SA = 55 I 



Figure 3. — The relationship between measured soil splash eroded into the bottom pan^ 

 rainfall intensity , slope steepness ^ soil bulk density , and the percent of soil 

 particles and water-stable aggregates between 61 and 2^000 microns ^ SA^ (R^=0. 97) . 

 The numbers at the comers of each surface indicate the amount of soil splash in 

 grams. Figujre ZA shows the relationship for three values of bulk density and an 

 SA of 55.1 percent; figure 3B is similar except SA is 81.9 percent. 



the percent sand-size material (not necessarily sand grains) is also directly related 

 to raindrop erosion. This is illustrated by comparing figure 3A with figure 3B. As 

 the proportion of sand-size material increases from 55.1 to 81.9 percent, the weight of 

 soil eroded by raindrop splash also increases. 



The average and maximum absolute deviations from regression were 32.9 g. and 

 79.9 g. , respectively. The mean weight of soil eroded by raindrop splash was 249.0 g. 



If the two soil factors, bulk density and proportion of sand-size material, are not 

 included in the interaction model, the resulting is 0.82. This means that the slope 

 steepness-rainfall intensity interaction accounted for 82 percent of the variance 

 associated with soil- splash erosion; soil bulk density and the proportion of soil 

 material in the sand-size range accounted for approximately 15 percent of the variance. 



The proportion of total splash going dou-nhill is quite difficult to measure, but 

 can be estimated on a rational basis (Ekem 1951). On a horizontal soil surface, the 

 soil splash resulting from raindrop impact should be equally divided in all directions. 

 However, assume a unit force of raindrop impact strikes an inclined soil surface in a 

 vertical plane. This impulsive force will result in two component forces, one parallel 

 to the slope in a downhill direction, the second normal to the slope (fig. 4). 



7 



