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Correlation between media physical and chemical properties and measured soil loss rates under rainfall at a range of slopes (%) for soils, overburdens, and soils and overburdens together
Data for the overburdens showed very different correlations with media properties than data for the soils.
The variation in correlation coefficients at different slopes found for the soils was not repeated for the overburdens. For example, the correlations with clay content at 5% and 30% slope for the overburdens are similar, at 0.81 and 0.72, respectively.
Increasing rock content was consistently correlated with decreasing erosion rates, at all slopes and for both soils and overburdens. This reflects the significant effect of rock on surface processes (Poesen et al.
The correlations with properties for soils, overburdens, and soils and overburdens together are listed in Table 5.
Correlation coefficients between media properties and rill erodibility calculated from Eqn 6 for soils, overburdens, and soils and overburdens together For property definitions see headnote of Table 2 Media properties Soils(A) Over- Soils and burdens(B) overburdens(C) EC -0.30 -0.13 -0.41(*) PH -0.07 0.00 -0.27 CEC -0.18 -0.09 -0.25 ESP 0.34 -0.52(*) -0.18 GWC -1.5 (kPa) -0.27 -0.27 -0.26 -0.01 (kPa) -0.22 -0.20 -0.17 SS ([m.sup.2]/g) -0.27 -0.27 -0.28 D2 -0.24 -0.38 -0.39 D20 -0.47(*) -0.39 -0.54(***) OC -0.23 n.d.
Overburdens containing [is greater than] 30% of competent rock can therefore be considered to be relatively stable with respect to rill erosion--at least for the flow conditions tested in this study.
Table 6 shows the correlations between erodibility (rill and interill) and texture size classes for soils and overburdens. For rill erodibility, correlations are increasingly negative for size classes approaching the 0-20 [micro]m class and increasingly positive approaching the 20 [micro]m-10 mm size class.
Tabulated values represent the correlation coefficient between erodibility and the particle size interval for overburdens (above diagonal) and soils (below diagonal) given by the column and row headings.
For interill erodibility the soils and overburdens are related to texture in very different ways.
In summarising the texture and erodibility data, it appears that rill erodibility is negatively correlated with particle classes [is less than] 20 [micro]m and higher than about 5-10 mm for both soils and overburdens. Interill erodibility is related to texture in different ways for soils and overburdens.
For overburdens, positive relationships with the clay content and the silt and clay dispersion ratio were found for interill erodibility.