## DESCRIPTION

r.uslek calculates the USLE K factor, that is the Soil Erodibility Factor. It takes input of soil texture classes (sand, clay, silt) and organic matter, all in range of [0.0-1.0]. The FAO World Soil CD documentation was used to produce the conversion system between soil textures and soil classes. The soil classes are in number of 12 and apparently come from a USDA publication of 1951 (p.209). Once the soil classes have been identified (by vector cross-products tests), a general conversion table was applied for transforming soil classes into K factor.

## NOTES

r.watershed provides for USLE L, S, LS factors.

## EXAMPLE

Calculate the USLE K factor (synthetic values, North Carolina sample dataset):

    # NC data: simulation
    g.region rural_1m -p

    r.mapcalc "sand  = 0.11"
    r.mapcalc "clay  = 0.47"
    r.mapcalc "silt  = 0.42"
    r.mapcalc "organ = 0.0136"

    r.uslek psand=sand pclay=clay psilt=silt pomat=organ output=usle_k
    r.univar usle_k
    # Result: uslek = 0.25

Example with small variations (condition: d_sand + d_clay + d_silt => 1.0)

    # NC data: simulation
    r.mapcalc -s "sand_r = rand(0.09,0.13)"
    r.mapcalc -s "clay_r = rand(0.45,0.49)"
    r.mapcalc -s "silt_r = rand(0.40,0.44)"
    r.mapcalc -s "organ  = rand(0.01,0.70)"

    r.mapcalc "temp_sum = sand_r + clay_r + silt_r"
    r.mapcalc "sand = sand_r / temp_sum"
    r.mapcalc "clay = clay_r / temp_sum"
    r.mapcalc "silt = silt_r / temp_sum"
    r.mapcalc "test = sand + clay + silt"
    r.info -r test
    g.remove -f rast name=sand_r,clay_r,silt_r,temp_sum,test

    r.uslek psand=sand pclay=clay psilt=silt pomat=organ output=usle_k
    r.univar usle_k
    # Result: uslek =  variable values

## SEE ALSO

r.usler, r.watershed

## AUTHORS

Yann Chemin, SIC-ISDC, Turkmenistan

Last changed: $Date$