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AOL MOL I "M tift M n MPM a IN a a a all a SOIL EROSION WORKSIIEET Geography Gersmehl t ' Soil erosion can occur only when wind or rain strikes an exposed PERCEtIT S L 0 P E L E iI G T II 1 N If E i E R S and erodible soil on a suitable sloptlt-The Universal Soil loss SLOPE° 25 50 100 150 200 750 300 400 500 6ft 7- '90' Equation Is a tool for predicting street (not gully) erosion due .4 0.5 0.4 0. 0 0.1 o.z o.3 0.3 0.4 4 to rainfall -- It Is based on lite fact that erosion depends on 2 2 0.3 0.5 0.7 0.8 0.4 0.4 1.o 0.I 1.2 the "cooperation" of at least five different factors: 6 0.6 0.9 1.2 1.5 1.1 1.9 2.1 2.4 2,7 3.0 3.3 34 R - the Intensity of rainfall expected In a region a,--- 0.9 1.3 1.8 2.2 2.6 2.9 3.1 3.6 4.0 K - the Inherent erodiblilty of the soil on the site 10 1.3 1.6 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 5.1 6.6 1.4 C - the protective cover of living or dead vegetation 14 2.1 3.011.4.2 5.2 6.0 6.7 7.3 8.5 9.5 P - the erosion-control practices•of the land user 16 2.6 3.7 5.3 6.4 1.4 8.3 9.1 11 12 The erosion that is likely to occur under a given combination of 18 3.2 4.S 6.4 7.8 9.1 10 11 13 IS conditions Is determined by looking up the five factors on these 20 3.8 5.4 7.1 9.4 11 12 14 16 to tables and map and then multiplying them together, for example, suppose a farmer In central Illinois (R a 400) uses a rotation of Percent hoops is equal to the overticalne change In meters per 1fe corn and soybeans with some residues left on the land (C - 0.30). meters of horizontal distance; one aster Is appro.lmately 3.3 fact The sandy loam soil has 3% humus (K = 25). the field has a 4% slope that Is *150 meters long (S = 0.8), and lite 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 - ORGANIC VATIER between 20 and 30 metric tons per hectare per year (multiply by SOIL iEXIURE 0% 31 61 R E S I D u E C o Y E R 0.44 to get lite answer in short tons per acre, round off to one coarse sand .06 .04 .02 slgnlficant figure to be honest about the method's accuracy, and medium sand .12 .09 .06 LAND USE none 1/4 3/4 , S_.10 smooth bare ground 1.0 .60 .20 I remember lilac an Inch of soil weighs a hundred tons per acre). loamy sand .16 fine Sano 20 <J2 .%DO rough bare ground .10 ,40 .15 loamy fine sand .2S .20 AS soybeans or cotton .60 .35 .20 3.7 Estimate the sheet erosion from a 200-meter 8% slope withcontinuous corn .50. .25 :10 ' an norganic'loam In central Alabama, If the farmer grew cotton flne3an0yaandy loam.loam • .30. .30 .25.25 .20 corn-soy rotation .55 .30 .IS and let cattle graze the residues on contour terraces (the most loam .40 .35 .30 small grains .25 10 AS expensive and effective erosion-control practice you could use slit loam .55 .45 .35 corn-grain rotation .35 .20 .07 and still make money In a normal year). silt .65 .SS .45 legumd-grass hay I$ o6 .03 slily clay loam .45 .3k .25 corn-graln-nay rot. .20 .10 .05 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 JS .10 overgrazed pasture .25 .10 .05 farming techniques that were inferior to those In the Midwest? clClay .25 .20 .IS ungrazed grassland •06 .03 .01 grazed forest .00 .04 .02 Decrease the K-factor by about 1/S dense forest .03 .01 .002 for good soil structure; Increase it by 1/S for poor structure. Residue cover should be evaluated In terms of Its ability to: t00 a) remain In place during high winds 100 200 b) protect the surface from rain Impact c) Impede the do.nslope movement of water les$ r EROS ION - Coll T ROl P R A C 1 ICE PERCEui than SLOPE STRAIGHT COiIOUR C011-51RIP C011-SiRIP COiIOUR 100 400 UP IIItLS PLOWING ROW/GRAIII ROW/NAY ICRAACE _ 2 1.0 0.60 0.40 0.30 0.20 4 600 6 1.0 O.SS 0.40 0.30 0.20 _ f 8 1.0 0.60 0.45 0.35 0.25 12 1.0 0.70 0-50 0.40 0.30 s- 16 1.0 .11 0.80 0.60 0.45 0.35 � 800 20 1.0 i 0.90 0.70 0.50 0.40 1 1 _ factors for erosion-control practices are valid only If the terraces or contour strips are designed and built property �• ,n' n?r 1000' ,\