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III. Predicting Soil Loss

III. Predicting Soil Loss. Why?. Putting the Pieces Together. Understanding what makes soil vulnerable Texture differences (silts vs clays vs organic matter) Climatic conditions (high wind, intense rainfall) Lack of cover Steep slopes. Putting the Pieces Together.

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III. Predicting Soil Loss

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  1. III. Predicting Soil Loss Predicting Soil Loss

  2. Why? Erosion & Sedimentation

  3. Putting the Pieces Together Understanding what makes soil vulnerable Texture differences (silts vs clays vs organic matter) Climatic conditions (high wind, intense rainfall) Lack of cover Steep slopes Erosion & Sedimentation

  4. Putting the Pieces Together Understanding what can minimize erosion We’ll spend the rest of the semester talking about management practices (structural and non-structural) that help minimize erosion for different land uses Erosion & Sedimentation

  5. Models Have you worked with models? Erosion & Sedimentation

  6. Prediction Models Help in communication of levels of soil erosion vulnerability Helps identify practices to protect soil and water resources Create a menu for the land owner Erosion & Sedimentation

  7. How Much is Too Much? Tolerable Soil Loss Erosion & Sedimentation

  8. How Much is Too Much? Tolerable Soil Loss – maximum level of soil erosion that will permit a high level of crop productivity to be sustained economically and indefinitely ‘T’ Erosion & Sedimentation

  9. Tolerable Rates T ranges from 1 – 5 tons / acre – year T values are assigned for each soil series As it turns out > 5 tons / acre – year is the‘how much is too much’ For fragile soils, sometimes 1 ton / acre – year is too much Erosion & Sedimentation

  10. Tolerable Rates Recall the 4 factors affect T: • Depth of soil • Type of parent material • Productivity of surface soil and subsoil • Amount of previous erosion Erosion & Sedimentation

  11. Soil Loss Models Wind and Water Where would you use each? Erosion & Sedimentation

  12. References Soil and Water Conservation. Troeh. Chapter 6. Predicting Rainfall Erosion Losses - A Guide to Conservation Planning. Agricultural Handbook 537. Predicting Soil Erosion by Water. A Guide to Conservation Planning With The Revised Universal Soil Loss Equation (RUSLE). Agricultural Handbook 703. Revised Universal Soil Loss Equation Version 2. USDA Universal Soil-Loss Prediction Equation for Planning Resource Use and Management Systems. USDA-SCS Alabama, All Field Offices Technical Guide Section I-C-1, revised March 1985. Erosion & Sedimentation

  13. Wind Erosion Prediction Models Wind Erosion Prediction Equation WEQ Predicting Soil Loss

  14. Wind Erosion Prediction Equation Original equation based upon wind tunnel research Modified as new information developed and new factors could be included Erosion & Sedimentation

  15. Wind Erosion Prediction Equation WEQ is an empirical equation Based upon observed results obtained over a range of test conditions Mathematical formulas developed based upon these results Erosion & Sedimentation

  16. Question If you were to develop a model to predict wind erosion, what factors would you enter into the model? What factors would contribute to increased or decreased wind erosion? Erosion & Sedimentation

  17. Wind Erosion Prediction Equation E = ƒ(I K C L V) E = predicted annual soil loss in tons/acre/yr ƒ is a notation that a relationship exists between erosion and the factors in parenthesis Erosion & Sedimentation

  18. Wind Erosion Prediction Equation E = ƒ(I K C L V) I = Soil Erodibility Factor Potential annual soil loss Wide, Unsheltered, Isolated field Bare, smooth, noncrusted surface Erosion & Sedimentation

  19. Wind Erosion Prediction Equation E = ƒ(I K C L V) K = soil ridge roughness factor Surface roughness from: Cloddiness of surface Ridges Vegetative cover Clods or ridged surfaces are less erosive Erosion & Sedimentation

  20. Wind Erosion Prediction Equation E = ƒ(I K C L V) C = climatic erosiveness factor Related to Wind speed Surface soil moisture Temperature Affects detachment and transport directly Influences plant growth and residue cover indirectly Erosion & Sedimentation

  21. Wind Erosion Prediction Equation E = ƒ(I K C L V) L = width of field factor the unsheltered distance along the prevailing wind direction across the area evaluated multiply the height of a barrier by 10 to determine shelter effect subtract this from the distance of the area traversed by the wind 1 Mile ½ Mile Prevailing Winds in March Erosion & Sedimentation

  22. Wind Erosion Prediction Equation E = ƒ(I K C L V) Which way is the wind blowing? Preponderance describes the proportion of wind parallel to prevailing wind direction as opposed to forces perpendicular to prevailing wind direction 1 = no prevailing direction 2 = twice as much erosive force in prevailing direction as in perpendicular to prevailing wind direction 1 Mile ½ Mile Prevailing Winds in March Erosion & Sedimentation

  23. Wind Erosion Prediction Equation E = ƒ(I K C L V) V = vegetative cover factor Depends on Amount of dry matter Texture Living or dead Standing or flat flattened wheat straw is standard term normally used is small grain equivalent Erosion & Sedimentation

  24. Is there a quicker way? A ‘shortcut’ was proposed by Soil Conservation Service specialists Wind Erodibility Groups (WEG) (Table 6-15, 167) No sieving necessary Erosion & Sedimentation

  25. Erosion & Sedimentation

  26. Wind Erosion Prediction Equation Changes in management can be applied to bring down the estimated soil erosion by wind. What changes would you make to reduce estimated soil loss? Erosion & Sedimentation

  27. Wind Erosion Prediction Equation Limitations of WEQ Estimates are in soil loss per year Soil erosion and the values of I, K, C, L and V change over the year WEQ was developed for the Great Plains Some of estimates not valid for other areas Has been modified some other locations Erosion & Sedimentation

  28. Wind Erosion Prediction Models Wind Erosion Prediction System WEPS Predicting Soil Loss

  29. Wind Erosion Prediction System (WEPS) In process of refinement Designed to replace WEQ Being field tested by NRCS Predicts soil erosion based upon simulation of fundamental processes controlling wind erosion Continuous, daily time-step wind erosion model Erosion & Sedimentation

  30. Wind Erosion Prediction System (WEPS) Provides more information than WEQ Abrasive damage to crops Soil productivity changes Off-site deposition Erosion calculations made upon grid Two dimensional WEQ calculates based upon line transect Erosion & Sedimentation

  31. Wind Erosion Prediction System (WEPS) Requires lots of data 4 databases Climate Soils Management Crops and Decomposition Erosion & Sedimentation

  32. Wind Erosion Prediction System (WEPS) More information is available at http://www.weru.ksu.edu/weps/ The software may be downloaded from this site Erosion & Sedimentation

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