Estimating Soil Erosion in Tennessee Using the Universal Soil Loss Equation

Transcription

1 University of Tennessee, Knoxville Trace: Tennessee Research and Creative Exchange Research Reports AgResearch Estimating Soil Erosion in Tennessee Using the Universal Soil Loss Equation University of Tennessee Agricultural Experiment Station John G. Graveel Ricky E. Lambert Follow this and additional works at: Part of the Agriculture Commons Recommended Citation University of Tennessee Agricultural Experiment Station; Graveel, John G.; and Lambert, Ricky E., "Estimating Soil Erosion in Tennessee Using the Universal Soil Loss Equation" (1986). Research Reports. The publications in this collection represent the historical publishing record of the UT Agricultural Experiment Station and do not necessarily reflect current scientific knowledge or recommendations. Current information about UT Ag Research can be found at the UT Ag Research website. This Report is brought to you for free and open access by the AgResearch at Trace: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Research Reports by an authorized administrator of Trace: Tennessee Research and Creative Exchange. For more information, please contact

2 5 Cf/,5 sity of Tennessee r'iu.?- 'tural Experiment Station,9~' /~ Research Report November 1986 Estimating Soil Erosion in Tennessee Using the Universal Soil Loss Equation Ricky E. Lambert

3 Estimating Soil Erosion in Tennessee Using the Universal Soil Loss Equation John G. Graveel and Ricky E. Lambert /,,/ University of Tennessee Agricultural Experiment Station

4 Estimating Soil Erosion in Tennessee Using the Universal Soil Loss Equation John G. Graveel and Ricky E. Lambert* Loss of topsoil by erosion presents a significant limitation to sustained agricultural production in Tennessee. Soil loss from Tennessee agricultural lands averages 10 tons per acre per year by sheet and rill erosion on the 5.6 million acres of cropland in the state (USDA-Soil Conservation Service, 1982). A total of 55.9 million tons of soil were eroded from Tennessee cropland in 1982 representing 70% of the state's annual soil loss of over 80 million tons from all sources (USDA-Soil Conservation Service, 1982). Effects of erosion are twofold. First, erosion reduces soil productivity by removing soil nutrients, degrading soil structure, and decreasing soil water holding capacity and plant rooting depth (Frye et al., 1982). Second, sediment, the end product of erosion, is a major source of water pollution. Among the environmental problems caused by sedimentation are the silting-in of stream channels and reservoirs, restricted stream flow that increases flood hazards, and impaired water quality due to sediment transport of nutrients and pesticides (Johnson and Moldenhauer, 1970; Rao et al., 1984; Nelson and Logan, 1984; Keeny, 1984). The Universal Soil Loss Equation (USLE) has been developed to estimate the rate of soil loss due to sheet and rill erosion on cultivated fields. The USLE provides a method for predicting long-term average annual soil losses under specific physical conditions, tillage practices, and cropping systems (Wischmeier and Smith, 1972; 1978). Evaluation of combinations of conservation practices and cropping management systems are easily made using the USLE: A = R x K x LS x C x P where A = the computed soil loss per unit area in tons per acre per year. R = the rainfall factor, which is the localized expected value of the rainfall-erosion index that incorporates both maximum 30-minute intensity and total kinetic energy of individual storm events averaged over a 22-year period. K = the soil erodibility factor, which is the soil loss rate per erosion index unit for a specified soil on a unit plot. A unit plot is 72.6 ft long, with a uniform lengthwise slope of 9%, in continuous fallow, tilled up and down the slope. LS = the length and steepness of slope factor (a graph has been developed to give the combined effects of these two variables). LS can also be evaluated by LS = (A -;.-100)x ( s s 2 ) where A is the field slope length in feet and s is the percent slope (Wisch me i- er and Smith, 1972). C = the cover and management factor, which is the expected ratio of soil loss under the conditions of a specific cropping system to soil loss from a clean-tilled field under continuous fallow. If the land is kept fallow, C= 1. P = the conservation practice factor, which is the ratio of soil loss with a specified erosion control practice * ASSISTANT PROFESSOR AND GRADUATE RESEARCH ASSISTANT, RESPECTIVELY, DEPARTMENT OF PLANT AND SOIL SCIENCE (KNOXVILLE). 3

5 like contouring, contour stripcropping, or terracing to that with straight row farming up and down the slope. If up and down slope field operations are used, P = 1. Modeling of soil erosion under specific field situations can be obtained using the USLE.An interactive USLEprogram was developed by Schneider et al., 1983 at Purdue University and can be used for evaluating the basic principles of erosion control. This program has been modified and adapted to Tennessee. The program allows an individual to provide information for specific situations (cropping system, soil type, location, and conservation practice) and to obtain easily and rapidly data on the consequences of their choices, reflected in tons of soil loss per acre per year. If the soil loss is greater than the tolerable loss, alternative cropping management systems and conservation practices which will result in an acceptable rate of erosion are offered. Soil loss values obtained using the USLE are compared to acceptable soil loss tolerance values developed by the USDA Soil Conservation Service. The USLE program reviews the factors affecting erosion and allows the individual to select a soil (establish the K factor) and choose the location (fix the R factor). Once these factors are established, the user is provided the effects of slope, cropping system, and conservation practices on erosion losses. Selected screen displays for predicting soil loss from a Memphis silt loam are shown in Figure 1: 1. The USLE equation is displayed and each variable in the equation is defined (Figure 1a). 2. A rainfall factor map (isoerodent lines) for Tennessee is displayed (Figure 1b). Isoerodent lines connect points of equally erosive average annual rainfall. The user selects the area and corresponding R value. 3. A table of soil erodibility factors (K)for 176soil series is displayed (Figure 1c)and the user selects the K factor for the soil of interest. 4. A graph of the relationship between length and steepness of slope is displayed (Figure 1d).The user enters the slope percent and length for a specific location and the LS factor is calculated for the relationship defined above. 5. After the R, K, and LS values are determined, the predicted soil losses for a continous fallow condition tilled up and down the slope, with no cropping or conservation practices (Figure Ie) is evaluated. 6. A table of cropping systems, conservation practices and corresponding C values for Tennessee is then displayed (Figure H). The user can select a C value from this table or extract an average annual C value from the cropping-management factors listed in Tennessee Agricultural Experment Station Bulletin 418, "Soil Losses in Tennessee Under Different Management Systems" by Jent et al., (1967). 7. A list of conservation practices is displayed (Figure 19).The user selects the appropriate support practice, i.e., contouring, contour stripcropping, or terracing combined with contouring. If no special practice is selected, P = The conservation practice is defined and the effectiveness of the support practice is discussed (Figure 1h). 9. The average annual soil loss (A)is calculated compared to T (tolerable soil loss) and the results displayed (Figure li). 10. If the soil loss is excessive (i.e., A is greater than T) too much soil is being lost for sustained productivity. The user is then asked to reduce soil loss by changing the cropping management factor or the erosion control practice until a tolerable soil loss is achieved. 11. The magnitude of the erosion problem is then pointed out and suggestions are made to the user concerning selection of an appropriate system. This program could be used as an effective tool by Vocational Agriculture teachers and County Extension Agents for instructing students about soil erosion under specific field situations. The USLE program is being used in the beginning soils courses at the University of Tennessee to improve learning and understanding of the many factors involved in the control of soil erosion. Since the program is interactive, students can not only select information on specific cropping systems and conservation practices, but the consequences of their choices are reflected immediately in the annual rate of soil loss. Alternate approaches then can be presented and considered. Average annual soil loss values obtained from this program can be used to assess the relative erodibility of a specific soil under various combinations of cropping and management systems. 4

6 Figure 1. Selected screen displays for predicting the annual rate of soil loss in tons per acre per year from a Memphis silt loam on a 5% slope, 200 ft. in length where conservation tillage (chisel plowing) is used in continuous grain sorghum planted on the contour in Jackson, Tennessee. Figure la. The universal soil loss equation. 5

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8 Figure lc. Soil erodibility factors (K values) for selected soils in Tennessee.

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10 Figure Ie. Preliminary estimate of soil loss under a clean-tilled continuous fallow condition. 9

11 10 Figure If. Cropping systems, conservation practice and corresponding C values for Tennessee.

12 Figure Ig. Conservation practices (Pl.

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14 Figure Ii. Average annual soil loss (A)compared to tolerable soil loss (T)under specified cropping and management systems. 13

15 REFERENCES Frye. W. W., S. A. Ebelhar, L. W. Murdock, and R. L. Blevins Soil erosion effects on properties and productivity of two Kentucky soils. Soil Sci. Soc. Am. J. 46: Jent, C. H., F. F. Bell, and M. E. Springer Predicting soil losses in Tennessee under different management systems. Univ. of Tenn. Ag. Exp. Sta. Bull Johnson, H. P., and W. C. Moldenhauer Pollution by Sediment: Sources and the detachment and transport processes. In T. L. Willrich and G. E. Smith (eds.) Agricultural practices and water quality. Iowa State University Press, Ames, Iowa. Keeney, D. R Transformations and transport of nitrogen. In F. W. Schaller and G. W. Bailey (eds.) Agricultural management and water quality. Iowa State University Press, Ames, Iowa. Nelson, D. W., and T. J. Logan Chemical processes and transport of phosphorus. In F. W. Schaller and G. W. Bailey (eds.) Agricultural management and water quality, Iowa State University Press. Ames, Iowa. Rao, P. S. C., P. Nkedi-Kizza, J. M. Davidson, and L. T. Ou Retention and transformations of pesticides in relation to nonpoint source pollution from croplands. In F. W. Schaller and G. W. Bailey (eds.) Agricultural management and water quality. Iowa State University Press, Ames, Iowa. Schneider, A. K, G. E. VanScoyoc, D. E. Driscoll, and W. W. McFee Soil loss: review and practice using the universal soil loss equation (USLE). Computer program. Agronomy Department. Purdue Univ. USDA-Soil Conservation Service National resources inventory. Tennessee state report. Wischmeier, W. H., and D. D. Smith Predicting rainfall erosion losses from cropland east of the Rocky Mountains. USDA Agr. Handbook 282. Wischmeier, W. H., and D. D. Smith Predicting rainfall erosion losses. USDA Agr. Handbook