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UIUC NRES 201 - Laboratory 3B Circular1220(1)

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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 of Agriculture 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 of 11 7 tons 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 tillage would 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 half times 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 Illinois farmland Although the soil and water conservation dis tricts are delegated the task of administrating the erosion control program it is as of November 1983 still voluntary There is however a clearly defined complaint process It is always possible that the program will become mandatory if the voluntary approach does not work The Universal Soil Loss Equation USLE The Universal Soil Loss Equation USLE provides a convenient way for you to estimate the rate of soil loss on your land so that you can see how that rate compares with your district s standards The USLE takes into account the major factors that influence soil erosion by rain fall rainfall patterns soil types slope steepness and management and conservation practices It was developed by the Agricultural Research Service the state experiment stations and the Soil Conservation Service SCS using research data from many research stations including work at Dixon Springs Urbana and Elwood Illinois More than 10 000 plot years of data were analyzed and used to develop the equation in the early 1960s Additional data mainly from rainfall simulator plots have been added to the equation in the latest revision Most of the recent data covers conservation tillage reduced tillage till plant and no till systems The USLE represents the average annual rate of soil loss due to splash sheet and rill erosion It does not estimate soil erosion from gullies or stream banks or the amount of sedi ment reaching streams Moreover the equation only gives the estimated average annual splash sheet and rill erosion for the specific field segment for which you have determined the appropriate factors It will not reflect the aver age soil erosion rate for the entire field unless 2 the segment you chose represents the field In general however you should not select a


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UIUC NRES 201 - Laboratory 3B Circular1220(1)

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