(6)
where X is Ln [crushing energy (J kg-1)] with lower limit 0.1.
The abrasion coefficient of aggregates and vertical abrasion flux simulated by SWEEP as a function of aggregate crushing energy for the four soil types are shown in Figure 9a and b. Both relationships appeared to be nearly logarithmic. However, a linear function provided a good fit to the data. The abrasion coefficient of aggregates and vertical abrasion flux decreased with increasing aggregate crushing energy. This trend was consistent with previous studies for a range of crushing energies (e.g., Hagen et al,1993; Zobeck, 1991b). Nonetheless, different regression coefficients suggest that the rate of change in abrasion coefficient and abrasion flux with an increase in crushing energy varied among soil types. The rate of change in simulated abrasion coefficients and abrasion fluxes with crushing energy was higher for the two sandy loams than two silt loams. These effects were consistent with measured soil loss.
The abrasion coefficient of aggregates and vertical abrasion flux simulated by SWEEP as a function of clay amendment for the four soil types are shown in Figure 10a and b. Both relationships appeared to be statistically significant except the relationship between vertical abrasion flux and clay amendment for Farrell sandy loam (Figure 10b). The SWEEP simulated abrasion flux for the four soil types was reduced at least 29% relative to a surface devoid of clay amendment.