1Estimating Soil Erosion Losses Circular 1220Excessive soil erosion in Illinois Cropland 40% 9.6 m acres Pastureland 23% 0.7 m acres Woodland 16% 0.6 m acresAverage cropland (in excess of T) = 11.7 tons/acIllinois Erosion Control Program 1/1/1983 4 times T 1/1/1988 2 times T 1/1/1994 1 ½ times T 1/1/2000 1 times T2Soil Erosion:Universal Soil Loss Equation (USLE)Revised Universal Soil Loss Equation (RUSLE)Water RKLSCPR Rainfall (intensity and amount, how erosive it is)K Factor for soil erodibility (silt most erosive)LS Slope factors (length and steepness)C Cropping factor (more cover is better) P Practices (conservation, terraces, strip cropping, etc) RUSLE Parameter basicsR factor; Soil rainfall erodibility factor (ft-ton in/acre yr) (was joules/ha) (Ranges in US from 0-600)K values; Soil erosion susceptibility (ton ac h/100 ac ft-ton in) (was mt/joules) (Range from 0.007 to 0.69)LS topographic factor; length and steepness (Range 0.25->11)C factor; Cover and cropping system, ratio eroded compared to that expected if soil kept bare-(Range- CS, fall till: 0.53 to 0.001 complete cover)P factor; crop practices, practice support factor (Typically 0.5-0.9)3Example 2 Perry county, Ava silt loam, 5% slope, 200 ft long, slightly or moderately erosion R value for Perry county is 220 (fig. 1) K value is 0.43 (Table 1) LS value is 0.76 (Table 3) T value is 4 Tons/acre R * K * LS = A 220 * 0.43 * 0.76 = 71.9 tons/acExample 2 (con’t) C value for Perry County (Table 6 (could be 4 or 5). Check Fig. 2 to see which table to use. C = 0.31 see footnote *1.2 for medium management C = 0.37 Corn & soybean rotation, 30” rows Conventionally tilled & spring plowed Medium level of management Corn yield = 75 bu/ac,soybean 33 bu/ac4Example 2 (con’t)220 * 0.43 * 0.76 * 0.37 * 1 = 26.6 tons/acP (Table 9) ResidueR * K * LS * C * P = A220 *0.43 * 0.76 * 0.37 * 0.5 = 13.3 tons/acExceeds T = 4 tons/acExample 2 (con’t) If changed to no-till (50% residue) then C = 0.11 * 1.2 = 0.13220 * 0.43 * 0.76 * 0.13 * 0.5 = 4.6 tons/ac5Example 2 (con’t) If no P change then you can solve for C substitute T for A C = T/ (R * K * LS * P)C = 5/ (220 * 0.43 * 0.76 * 0.5) = 0.14Need a cropping factor below this value.Erosion ClassesUSDA, NRCS Slightly eroded – soils that have lost less than 25% of the original A horizon or of the uppermost 20 cm if the original A horizon was less than 20 cm thick. Moderately eroded – soils that have lost between 25% and 75% of the original A horizon and material below (B horizon)6Erosion ClassesUSDA, NRCS (con’t) Severely eroded – soils that have lost 75% or more of the original A horizon material below the A horizon is exposed at the surface in cultivated areasErosion ClassesUSDA, NRCS (con’t) Erosion phases relate to a specific soil series Tama silt loam, 0-2% slopes, slightly eroded Tama silty clay loam, 4 to 7% slopes, moderately
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