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SO EROS 1011 WORKSHEET Geography Gersmehl L Soil erosion can occur only when wind or rain strikes an exposed S L O P E L E it G I f1 I n 11 E I E R S and erodible soli on a suitable sloptitl 'Tire Universal Soil Loss PEacEnt Equation Is a tool for predicting street not gully) SLOPE 25 so 100 150 200 250 300 400 500 7- ifoo P e ( g y) erosion due 2 0.1 0.2 0.3 0.3 0.4 0.4 0.4 0.4 0.5 to rainfall -- It Is based on the fact that erosion depends on the "cooperation" of at least five different (actors: A 0.3 0.5 0.7 0.0 0.9 0.9 1.0 1.1 1.26 0.6 0.9 1.2 1.5 1.) 1.9 2.1 1.4 1.1 3.0 3.3 3•(0 gion the Intensify of rainfall expected In a re K - the inherent efodibilily Of the soil on lire 511e a' - 0.9 1.3 1.8 2.2 2.6 1.9 3.1 3.6 4.0 S - the angle. 10 1.3 1.8 2.5 3.1 3.6 4.0 4.3 5.6 5.6 g geometry, and length of-the slope 12 1.) 2.1 3.3 A.1 4.7 5.2 S.1 6.6 ).A C - the protective cover of living or dead vegetation 14 2.1 3-011.4.2 5.1 6.0 6.) ).) 8.5 9.5 P - ►Ire erosion-control practices of the land user 16 2.6 3.1 5.3 6.4 1.4 0.3 9.1 It 12 The erosion that Is likely to occur under a given combination of 18 3.2 4.S 6.4 7.0 9.1 10 11 13 IS conditions Is determined by looking up the five factors on these 20 3.8 S.4 7.1 9.4 11 12 14 16 1e 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 equal to the vertical change In meters per 100 corn and soybeans with some residues left on the land (C a 0.30). meters of horilonta) distance; one meter Is approAlmately 3.3 feet The sandy loam soli has 3% humus (K s .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 You multiply the five factors together, the estimated erosion is - ORGAIIICILAll[R between 20 and 30 metric tons per hectare per year (multiply by SOIL 1ExIURE 01 31 61 044 to get the answer In short tons per acre, round off to one coarse sand .06 .04 .02 R E S 1 0 u E C o v E R signlfIC401, figure to be honest about the method's accuracy, and medium sand .12 .09 .06 LAND USE none 1/4 3/4 remember that an Inch of soil weighs a hundred tons per acre). fine sang 20 .15_.10 smooth bare ground$ 1.0 .60 .20 loamy tend .16 r.it A 08 rough bare ground .10 .40 .15 loamy fine sand .25 .26 .1S soybeajis or cotton .60 .35 .20 3,� Estimate the sheet erosion from a 200-meter OX slope with sandy loam .30 ' .25 .20 continuous corn .50. .25 :lo an fnorganlc'loam In central Alabama, if the farmer grew cotton Ao .35 .30 sma11 grains rotation .55 .30 .15 floe sandy loam 35 .30 .25 and let cattle graze the residues on contour terraces (the most loamy ns .25 .10 .05 expensive and effective erosion-control practice you could use slit loam .55 .45 .35 corn-grain rotation .3S .20 .07 and still make money In a normal year), slit .6S .55 .45 leguma-grass hay IS .06 .03 silty cloy loam .45 .35k .25 corn-graln-hay rot. .20 .10 .05 Does a comparison of these two situations support the popular sllty clay 35 (:30> .25 dry-farmed grain .40 .20 .10 textbook explanatlon of abandoned southern fields as products of sandy clay .20 .15 .10 overgrazed pasture .25 .10 .05 farming techniques that were inferior to those In the Midwest? clay loam .30 .25 .20 managed pasture .10 OS .02 clay .25 .20 .15 ungrazed grassland .06 .03 .01 Decrease the K-/actor b about 1/5 grazed forest .08 .01 .02 y dense forest .03 .01 .002 for good soil structure; Increase it Will by 1/S for poor structure. Residue cover should be evaluated In terms 100 of Its ability to: e) remain In place during high winds -� 100 200 b) protect the surface from rain Impact 06.dff c) Impede the do-nslope movement of water �� rV less P[a[Wt IR0510It - C 0 I I R 0 L PRAC I ICE � - _ _ _ l..�G��'t1S••�� than I (_ 1- 11� SLOPE 51RAIG111 COIIIOUR C011-S1RIP COII-S1RIP COIIIOUR 100 _ - l 400 UP HILLS PLOWMIG ROW/GRAIII ROU/rut TERRACE I 2 1.0 0.60 0.40 0.30 0.20 t \ l 4 1.0 0.50 0.35 0.25 0.15 \, , 600 8 1.0 0.60 0.45 0.35 0.25 - ---t �- 12 1.0 0.10 0.50 0.40 0.30 16 00 l 0.80 0.60 0.45 OAS Boo 20 l.o 0.90 0.70 0.50 0.40 100 }- '� factors for erosloo-control practices are valid only It the r terraces or contour strips are designed and built properly 200tL0000 1 '^10001 400 600