Vincent de Leijster

167 Appendices Adjustments and assumptions about the RUSLE method We used a visual soil surface assessment to estimate soil erosion potential, which has been proposed as an indicator for erosion control in coffee plantations (Blanco Sepúlveda and Aguilar Carrillo, 2015). Based on the soil surface properties, which we described in in the main text, we calculated the potential soil loss using the Revised Universal Soil Loss Equation (RUSLE), following (Renard et al., 1997). This approach uses the factors rainfall erosivity (MJ mm ha -1 h -1 ), soil erodibility (Mg h -1 MJ -1 mm -1 ), slope length (m), slope steepness (rad), cover management, and soil support, to calculate potential soil loss (Mg soil ha -1 y -1 ). We refer the reader to the appendix for more specific information about adjustments and assumptions in addition the RUSLE method. A = R · K · L · S · C · P (equation 5) Where R is the rainfall erosivity factor (MJ mm ha -1 h -1 ), K the soil erodibility factor (Mg h -1 MJ -1 mm -1 ), L the slope length factor (m), S the slope steepness factor (rad), C the cover management factor, and P the soil support factor. We obtained the factors for rainfall erosivity and soil erodibility from a soil erosion study on coffee that was conducted in the same study region (Hoyos, 2005). The slope length was obtained from spatial analysis using a digital elevation model taking the distance from the location of the farm to the top of the hill. The slope steepness was measured in the field. The cover management was obtained by multiplying five subfactors, namely, prior land use (PLU), canopy cover (CC), soil surface cover (SC), soil surface roughness (SR) and soil moisture (SM), following the formula: C = PLU · CC · SC · SR · SM (equation 6) Prior land use (PLU) was calculated using the following formula (Renard et al., 1997): PLU = C f · C b · exp[(-c ur · B ur ) + (C us · B us /C f Cuf )] (equation 7) Where Cf is the tillage factor (Cf=1, as tillage is not applied), Cb the subsurface residue constant (Cb=0.951; Renard et al., 1997), cur and cus are calibration coefficients indicating the impacts of the subsurface residues (cur=0.00199 and cus=0.000416; Renard et al., 1997), Bur and Bus are the mass density of alive and dead roots (Bur=450 and Bus=1325; Bakker et al., 2003), and cuf is the impact of soil consolidation on the effectiveness of incorporated residue (cuf=0.5; Renard et al., 1997). The canopy subfactor (CC) was measured in the field including the canopy height and cover (see 3.3.1.1). The soil surface cover subfactor (SC) was calculated with the following formula (Renard et al., 1997):