## 2 Materials and Methods
### RUSLE Model
#### Cover Management (C) Factor
(2018) recommended that pixels with negative values be adjusted to 0 and that pixels with values greater than 100 be adjusted to 100. As cited by [PERSON] et al. (2018), the following equations represent the empirical relation between the C-factor and the fractional vegetation cover for China:  
\[\mathrm{C(FVC)}=\left\{ \begin{array}{cl}1,&FVC=0\\ 0.6508-0.343\,\log FVC,&0<FVC<78.3\%\\ 0,&FVC\geq 78.3\%\end{array} \right. \tag{19}\]  
Support Practices (P) Factor  
In Crete, the main conservation support practices are contour farming (\(P_{c\!f}\)), stone walls (\(P_{sw}\)), and grass margins (\(P_{gm}\)) ([PERSON], 2016); thus, these three types of support practices were considered to estimate the P-factor according to the following equation:  
\[P=P_{cf}\times P_{sw}\times P_{gm} \tag{20}\]  
where \(P_{cf}\), \(P_{sw}\), and \(P_{gm}\) are the P-factor values for contour farming, stone walls, and grass margins, respectively. Contouring is a specific support practice applied only in croplands. The contour farming efficiency is influenced by the topographic slope. [PERSON] and [PERSON] (2018) assumed that contouring seems to be most effective on slopes ranging between 3 and 8 percent. As such, according to the slope gradient, respective P-factor values were assigned (Table 5). Commonly, stone walls and grass margins cause reductions in soil erosion rates by decreasing the velocity of the overland flow and sediment transport, respectively [1]. Dry stone walls are extensive landscape features in the Mediterranean preventing soil erosion, especially in hilly areas. In Greece, the density of stone walls exceeds 8% [19]. Grass margins are strips of principally uncultivated land with vegetation dominated by grasses or herbs. They are mainly located at the borders of fields, between cropped areas or neighboring roads and pathways [19]. Table 6 represents the density values of stone walls and grass margins along a transect (LUCAS database) and assigned P-factor (\(P_{\text{sw}}\) is the stone walls sub-factor and \(P_{gm}\) is the grass margins sub-factor) values for Europe. In order to evaluate the effects of these features on a study area, spatial interpolation process should be executed. According to the objective of the study, which was to define the spatial patterns of stone walls and grass margins, and by referring to previous studies, the kriging approach was used for spatial interpolation. In fact, this method provides a spatially homogeneous surface with a constant variance and mean [19]. In this study, the ordinary kriging was based on 12 observation points for the radius setting. As mentioned earlier and according to Equation (1), 5 different factors were organized in GIS raster grids with 10 m spatial resolution and then overlaid in the GIS environment. The final soil loss map was produced using the GISus-M plug-in module for ArcMap. This is an add-in for ArcGIS Desktop, which was built using an integrated development \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No of Features (SW or GM)** & **\% Sw** & **Psw** & **\% Gm** & **Pgm** \\ \hline
0 & 0 & 1 & 0 & 1 \\ \hline
1 & 83.33 & 0.707 & 100 & 0.853 \\ \hline
2 & 0 & 0.577 & 0 & 0.789 \\ \hline
3 & 16.66 & 0.5 & 0 & 0.750 \\ \hline
4 & 0 & 0.448 & 0 & 0.724 \\ \hline
5 & 0 & 0.408 & 0 & 0.704 \\ \hline
6 & 0 & 0.378 & 0 & 0.689 \\ \hline
7 & 0 & 0.354 & 0 & 0.677 \\ \hline
8 & 0 & 0.334 & 0 & 0.667 \\ \hline \textgreater{}8 & 0 & 0.317 & 0 & 0.66 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: P-factor values for the stone walls sub-factor (\(P_{\text{sw}}\)) and grass margins sub-factor (\(P_{gm}\)) for the LUCAS database [19]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Slope (\%)** & **Pcf** \\ \hline
1–2 & 0.60 \\ \hline
3–5 & 0.50 \\ \hline
6–8 & 0.50 \\ \hline
9–12 & 0.60 \\ \hline
13–16 & 0.70 \\ \hline
17–20 & 0.80 \\ \hline
21–25 & 0.90 \\ \hline \textgreater{}25 & 0.95 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: P-factor values for contour farming practices for different slope gradients [19].