•• •• ••••••••••••••••••••••••••••••••• •• •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• •••••••••• ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• Cooperative Extension Service.College of Agriculture ••Circular 1220 •• ••••• University of Illinois at Urbana-Champaign ••••••••••TABLE OF CONTENTS Illinois Erosion Control Program.... .. 1 The Universal Soil Loss Equation (USLE) 1 Rainfall (R) Factor.. ................................................... 2 Soil Erodibility (K) Factor............. 2 Slope Length and Steepness (LS) Factor........................ 3 Cropping and Management (C) Factor.......................... 3 Conservation Practices (P) Factor............. 5 Using the USLE 6 Working through Some Examples................................ 6 Solving the USLE for C 7 Getting Help 7 Tables 8-16 Appendix: How to Make and Use a Slope Gauge 17 Tables Table 1. Soil Erodibility (K) and Erosion Tolerance (T) Values for Specific Illinois Soils.. ... .......................................................... 8 Table 2. Soil Erodibility (K) Values for Certain General Soil Types..................... ..11 Table 3. Slope Length and Steepness (LS) Values for Specific Combinations of Length and Steepness. ................ ............................... . 11 Table 4. Cropping and Management (C) Values for Northern Illinois 12 Table 5. Cropping and Management (C) Values for Central Illinois 13 Table 6. Cropping and Management (C) Values for Southern Illinois 14 Table 7. C Values for Permanent Pasture, Range, and Idle Land. . 15 Table 8. C Values for Undisturbed Forest Land 15 Table 9. Conservation Practices (P) Values for Contour Farming and Contour Strip Cropping 16 Table 10. Values Used in Determining P Values for Terraces Built on Contour and Used in Combination with Contour Farming and Contour Strip Cropping ... 16 This circular was prepared by Robert D. Walker, Extension natural resources specialist, and Robert A. Pope, former Extension agron-omist, University of Illinois at Urbana-Champaign. The authors would like to thank Steve Probst, Soil Conservation Service, for his careful review and helpful suggestions. Information in this circular is based on Agricultural Handbook 537 published by the Science and Education Administration, U.S. Departmeat ofAgriculture, and generally corresponds with information contained in the Soil Conservation Service's Illinois Technical Guide.Excessive soil erosion occurs on 40 percent, or 9.6 million acres, of Illinois cropland. Erosion on this land exceeds the soil loss tolerances of one to five tons per acre annually, with a high of over 50 tons per acre and an average of11.7tons. In addition, 23 percent, or 700,000 acres, of pastureland and 16 percent, or 600,000 acres, of woodland have excessive soil erosion. The loss of valuable topsoil to erosion is compounded by the loss of plant nutrients and organic matter and by more difficulty in tilling since the soil becomes increasingly clayey as more subsoil is brought to the surface. But the problems of erosion are not confined to farm-land. The sediment that leaves fields often has an adverse effect on the water quality and condition of drainage ditches, lakes, reservoirs, and streams. Many types of problems arise: sediment decreases the storage capacity oflakes and reservoirs, clogs streams and drainage channels, causes deterioration of aquatic hab-itats, increases water treatment costs, and car-ries displaced plant nutrients. Illinois Erosion Control Program In response to the accelerated loss of soil productivity and to the off-the-farm effects of erosion, the state of Illinois has designed an erosion control program. The goal of this pro-gram is to reduce annual soil erosion losses on all agricultural land to one to five tons per acre by the year 2000 depending upon the soil type. This rate of erosion is considered the soil loss tolerance level (the T value). Where erosion exceeds the T value, soil is being lost so fast that the land's natural productivity is being dimin-ished. Table 1 lists the T value for most Illinois soils (all tables are given at the end of the text). The erosion control program is divided into intermediate goals, all leading up to the year 2000. To begin the program, the 98 soil and water conservation districts in Illinois devel-oped soil erosion standards for all soils in their districts. The districts' standards, which went into effect on January 1, 1983, were required to be at least as stringent as the state's guidelines, although some districts developed standards stricter than the state's guidelines. The state's guidelines are as follows: • By January 1, 1983, erosion on all farmland could not exceed four times the T value (4 to 20 tons per acre annually) established for the soil type. • By January 1, 1988, soil loss cannot exceed two times the T value (2 to 10 tons per acre annually). Where conservation tillagewould solve the erosion problem and the slope is less than five percent, however, soil loss must not exceed the T value (1 to 5 tons per acre annually). • By January 1, 1994, erosion on all farmland cannot exceed one and a halftimes T (1 Y:! to 7Yz tons per acre annually). • By January 1 of the year 2000, erosion cannot exceed the T value (1 to 5 tons per acre annually) on any