where Kr is rill erodibility (s m-1), τ is flow shear stress
(Pa), and τc is the critical shear stress (Pa). Previous studies
showed that root density had great influence on erodibility
of concentrated flow erosion (Mamo and Bubenzer, 2001a;
De Baets et al., 2006; De Baets and Poesen, 2010). For
comparison, the data from this study were divided into
14 groups according to root density (table 3), and the
relationship between rill erodibility and root density was
analyzed. It clearly showed that Kr decreased with an
increase in root density, especially when root density was
less than 2.4 kg m-3. Rill erodibility fluctuated around
0.08 s m-1 when RD was greater than 2.4 kg m-3. The mean
erodibility of rooted soil samples was only 22% that of the
control. The best fit between rill erodibility and root density
was (fig. 3):