Estimating Soil Erosion Losses Circular 1220 Excessive soil erosion in Illinois Cropland 40 9 6 m acres Pastureland 23 0 7 m acres Woodland 16 0 6 m acres Average cropland in excess of T 11 7 tons ac Illinois Erosion Control Program 1 1 1983 1 1 1988 1 1 1994 1 1 2000 4 2 1 1 times T times T times T times T 1 Soil Erosion Universal Soil Loss Equation USLE Revised Universal Soil Loss Equation RUSLE Water RKLSCP R 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 basics R 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 2 Example 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 ac Example 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 ac 3 Example 2 con t 220 0 43 0 76 0 37 1 26 6 tons ac P Table 9 Residue R K LS C P A 220 0 43 0 76 0 37 0 5 13 3 tons ac Exceeds T 4 tons ac Example 2 con t If changed to no till 50 residue then C 0 11 1 2 0 13 220 0 43 0 76 0 13 0 5 4 6 tons ac 4 Example 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 14 Need a cropping factor below this value Erosion Classes USDA 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 5 Erosion Classes USDA 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 areas Erosion Classes USDA 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 eroded 6
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