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IL EROSION WORKSHEET Geography Gersmehl L Sol) erosion can occur only when wind or rain strikes an exposed S L O P E L E N G T 11 I N H E T E R S and erodible soil on a suitable slo e. 'The Universa) Soil loss PERCENT p SLOPE 2S 60 100 150 200 250 300 400 500 Equation Is a tool for predicting sheet (not gully) erosion due to rainfall -- It Is based on the fact that erosion depends on 2 0.1 0.2 0.3 0.3 0.4 0.4 0.4 0.4 0.5 2 0.3 0.5 0.7 0.8 0.4 0.4 1.0 1.1 1.2 the cooperation of at least five different factors: 6 0.6 0.9 1.2 1.S 1.7 1.9 2.1 2.4 2.7 R - the Intensity of rainfall expected in a region 8=- 0.9 1.3 1.8 2.2 2.6 2.9 3.1 3.6 4.0 K - the inherent erodibillty of the soil on the site 10 1.3 1.8 2.5 . 3.1 3.6 4.0 4.3 5.0 5.6 S - the angle, geometry, and length of-the slope 12 1.7 2.3 3.3 4.1 4.7 5.2 5.7 6.6 7.4 C - the protective cover of living or dead vegetation 14 2.1 3.0 4.2 5.2 6.0 6.7 7.3 8.5 9.5 P - the eroslon-control practices of the land user 16 2.6 3.7 S.3 6.4 7.4 8.3 9.1 11 12 The erosion that is likely to occur under a given combination of to 3.2 4.S 6.4 . 7.8 9.1 10 I1 13 iS conditions Is determined by looking up the five factors on these 20 3.8 5.4 7.7 9.4 11 12 14 16 18 tables and map and then multiplying them together. For example, suppose a farmer In central Illinois (R = 400) uses a rotation of Percent slope Is radii to the vertical change Imeters per 100 corn and soybeans with some residues left on the land (C = 0.30). meters of horizontal distance; one meter Is approximately 3.3 feet The sandy loam soil has 3% humus (K 25), the field has a 4% slope that Is '150 meters long (S = 0.8). and the farmer plows up and down hill with no concern for conservation (P = 1.0). When ORGANIC MATTER you multiply the five factors together, the estimated erosion Is SOIL TEXTURE OX 3I 6S between 20 and 30.metric tons per hectare per year (multiply by C R E S I o u E C 0 Y E R 044 to get.the answer In short tons per acre, round off to one coarse sand .06 .04 .02 LAND USE none 1/4 3/4 signlflcant'figure to be honest about the method's accuracy, and medium sand .12 .09 .06 remember that an:inch of soil weighs a hundred tons per acre), fine sang .20 .15 .10. smooth Dare ground 1 .0 .60 .20 loamy sand .16 .12 .08 rough bare ground .70 .40 .15 loamy fine sand .25 .20 .IS soybeans or cotton .60 .35 .20 3,� Estimate the sheet'eroslon from a 200-meter 8% slope with continuous corn .. .50... .25 .10 I loam .30" .25 .20 corn-so :7 0 o an norganlc'loam in central Alabama, if the farmer grew cotton fine sandy loam, .3S .30 -25 y rotation .55 . ,.30 •15 f/ S and let cattle graze the residues on contour terraces (the most 1049 .40 .3S .30 small grains .25 .10 AS L ` H - •�^ expensive and effective erosion-control practice you could use silt loam .55 .45 .35 corn-grain rotation .3S .20 .07 and stili make money In a normal year), slit .65 .55 .4S legume-grass hay .15 .06 .03 ` = � 0 silty cly loam .45 .35 .25 corn-grain-hay rot. .20 .10 .05 a S ; 6 Does a comparison of these two situations support the popular silty clay .35 .30 .25 dry-farmed grain .40 .20 .10 textbook explanation of abandoned southern fields as products of sandy clay .20 AS .10 overgrazed pasture .25 .10 .05 farming techniques that were Inferior to those In the Midwest? clay loam .30 .25 .20 managed pasture .10 .05 .02 P a y clay .25 .20 .15 grazedeforrestsland .08 .01 02 Decrease the K-factor by about 1/5 dense forest .03 .01 .002 for good soil structure; Increase It by i/5 for poor structure. Residue cover should be evaluated In terms of Its ability to: 100 al remain In place during high winds ' 100 200 b) protect the surface from rain Impact c) Impede the downslope movement of water ~�� l EROS10H - C011TR0L PRACTICE less r PERCENT than ^ SLOPE STRAIGHT COiITOUR C011-STRIP CON-STRIP EOIIIOUR 100 400 UP HILLS PLOWING ROW/GRAI11 ROWJIIAY TERRACE r i 2 1.0 0.60 0.40 0.30 0.20 t 4 1.0 0.50 0.35 0.25 0.15 rl 600 6 1.0 0.55 0.40 0.30 0.20 8 1.0 0.60 0.45 0.35 0.25 12 1.0 0.70 0.50 0.40 0.30 .� 16 1.0 0.80 0.60 0.45 0.35 1-( 800 �° 20 1.0 0.90 0.70 0.50 0.40 / t -00 factors for erosion-control practices are valid only If the terraces or contour strips are designed and built properly 200 800100 400 600 l Figure 3