Predicting Soil Loss Control Programs Need methods of evaluating effectiveness of erosion control measures Soil Conservation Service SCS now NRCS Measure erosion losses from land to assess the effects of soil properties vegetation slope climate and other factors on the erosion process Farm plans use soil loss prediction equation Soil loss prediction equations were developed for both water and wind erosion Soil Loss Tolerance Soil Loss Tolerance con t Reduce erosion possible to prevent erosion Tolerable soil loss Maximum allowable rate of soil erosion which will permit the indefinite maintenance of soil productivity How much is a tolerable rate of soil loss Usually about 5 tons ac 11 mt ha for most deep loess soil in Illinois One metric ton of soil loss per hectare 0 075 mm 133 yrs 1 cm of soil Some Illinois soils have lost 0 5 m in 133 years Soil Development Using soil development rate Purdue Kohnke and Bertrand Y 0 36t0 561 or t 6 18Y Y depth of soil development T time year Rate of new soil development in years cm dt dY 11Y0 783 d 1st derivative dt dY the number of years it would take to form 1 cm of new soil from glacial till 1 cm in 11 years at 1 cm depth 1 cm in 230 years at 50 cm depth 1 cm in 405 years at 1 m depth 1 Soil Development con t Iowa Hallberg 1978 A horizon 31 cm deep development in 100125 years in 64 cm of deep fill materials National Runoff and Soil Loss Data Center Started at Purdue University Lafayette Indiana in 1954 by the Agricultural Research Service of USDA Contributions Establishment of rainfall erosion index accounted for a greater proportion of soil loss variation from storm to storm Method for evaluating the cropping management factor Development of Water Erosion Prediction Equation Zingy 1940 equation relating soil loss to percent slope and slope length Smith 1941 incorporated crop and conservation management factors Wischmeier and Smith 1965 Estimating sheet and rill erosion losses from cultivated fields for U S east of Rocky Mountains Universal Soil Loss Equation sheet and rill erosion only USLE Wind erosion A R K LS C P A estimated average annual soil loss mt ha R rainfall and runoff factor j ha K soil erodibility factor soil loss per unit of rainfall erosivity index from bare fallow on a 9 slope 22 1 m long mt j First thought to be offset by gains from neighboring fields up slope loss could still be excessive Stringent restrictions on erosion dictated by tolerable losses established to reduce pollution and sediment 2 USLE con t A R K LS C P con t LS slope length steepness factor dimensionless C cropping management factor versus land fallow dimensionless P erosion control supporting practice factor dimensionless Soil removal A Losses represent the gross amount of soil detached and transported including soil redeposited in depressions grassed waterways and rest of field Slope Factor LS Point where overland flow begins towards a waterway or to where slope decrease and sediment deposition begins L field slope length 22 1 m S slope gradient Soil removal A Losses represent the gross amount of soil detached and transported including soil redeposited in depressions grassed waterways and rest of field Rain erosion index R Erosion produced related to total energy e and maximum 30 minutes intensity I30 R sum of EI30 for all major storms in a year metric units for E are j ha representing either energy or work per unit area I30 can be measured in mm hr units omitted R K mt ha Soil Erodibility Factor K Converts units of R to amounts of erosion Standard plots 9 slope and 22 1 m long Relates soil properties to soil erodibility 3 Crop Management Factor C Crops intercepts rainfall reduce puddling of surface soil help maintain infiltration rate and slow runoff Crop Management Factor C con t Ration between the amount of soil lost under specific crop cover management conditions and that lost when the soil is fallow and cultivated up and down the slope at regular intervals 5 growth stages in order to evaluate protection Predicting Soil Loss for a Particular Field A R K L S C P 300 0 43 2 19 0 34 1 0 96 mt ha yr R K LS and T can be obtained from a knowledge of soil series slope gradient and length of slope 4