Soil Erosion


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I developed this set of slides for my Soil and Water Conservation class in Spring 2012

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Soil Erosion

  1. 1. A 4 trillion cubic meter slice through ~ 2 billion years of strata!! Erosion is a natural process !
  2. 2. Natural erosion rates (m/m.y. = meters per million years)
  3. 3. Cropland erosion rates = 0.6 mm/y
  4. 4. Natural vs. accelerated erosion globally Natural Erosion Accelerated Erosion acclerated erosion = accelerated by human activities
  5. 5. Impact of climate on natural erosion rates Brady and Weil (2002)
  6. 6. Variation in natural erosion rates
  7. 7. Intense thunderstormsprovide the desert areasof the Southwestern US with most of their meager annual precipitation.
  8. 8. What do you think this arroyolooks like during a thunderstorm?
  9. 9. Fortunately most of land surface not covered byvegetation is covered by desert pavement
  10. 10. Fortunately most of land surface not covered by vegetation is covered byor cryptobiotic crusts desert pavement
  11. 11. What created this?
  12. 12. Understanding water erosion processes 300 – 900 PSI 20- 40 feet / s 1) Detachment 2) Transport 3) DepositionBrady and Weil (2002)
  13. 13. Detachment Transport Deposition
  14. 14. Manobolo RiverDetachment estimates >> river sediment loads Why ?? Most sediment is deposited within the same landscape
  15. 15. Deposition zone Elevated SOM and nutrient levels
  16. 16. Sheet erosionBrady and Weil (2002)
  17. 17. Rill erosion Rills result from concentrated flow and can be filled by normal tillage operationsBrady and Weil (2002)
  18. 18. We had better dosomething before this rill turns into a gully.
  19. 19. Gully erosion Dad !!! I think the rill has turned into a gully!
  20. 20. From : Steve Groff sgroff@hughes.netSent : Thursday, June 29, 2006 5:49 AMHi Joel,We ended up with 14.8" of rain over a 4 day period. These picturesshow how my neighbor’s plowed fields look. The ditch was up to4 4" deep and averaged about 3 deep in a 400 section- that is nota typo! The staked tomato picture is on my side of the propertyline looking from that ditch-100 feet away. I did have a little bit oferosion but could find nothing over 1" deep…Steve
  21. 21. Fresh Market Tomatoes planted no-till into cover crops on Steve Groff’s farm
  22. 22. Neighbor’s conventional-till corn field ~100’ away
  23. 23. When a stream is straightened or widened, streambank erosion increases. Accelerated streambank erosion occurs until the stream reestablishes a stable size and pattern.Streambank erosion When land use changes occur in a watershed, such as clearing of land for agriculture or development, runoff increases. With this increase in runoff the stream channel will adjust to accommodate the additional flow, increasing streambank erosion.
  24. 24. Shoreline erosion As a boater, you can reduce shoreline erosion by reducing the speed and resulting wake from your boat, especially when the water level is above normal. Hydrologists estimate a wake 10” high is five times as destructive to the shoreline as a 5” wake and a wake that is 25” high has a destructive potential that is 30 times greater than a 5” wake.
  25. 25. Engineering properties of soil Liquid limit Brady and Weil, 2002 low Moisture content highWhen moistened to its liquid limit, a soil starts to flow.
  26. 26. La Conchita landslideOn January 14th 2005,250,000 cubic yards ofsoil flowed into the LaConchita neighborhooddestroying 13 housesand severely damaging23 others.
  27. 27. Slump
  28. 28. Creep
  29. 29. Major causes of accelerated erosion in Illinois Arrival of tractors and the moldboard plow Arrival of soybean as a major crop replacing oats Construction and Mining Highest rates
  30. 30. It looks like we have madelots of progress… but howmuch confidence should we have in these #s??
  31. 31. ―It is questionable whether there has ever been another perceived publicproblem for which somuch time, effort andmoney were spent in light of so littlescientific evidence.‖
  32. 32. History of the Universal Soil Loss Equation (USLE)During the 1940s and 50s, soil scientists in the Corn Belt region began todevelop quantitative methods of predicting soil loss. It was recognized thata soil loss equation would be a valuable tool for farm planning. In 1946, agroup of erosion specialists held a workshop in Ohio to reappraise thefactors previously used to predict erosion (slope and management) andadded a rainfall intensity factor. The National Runoff and Soil Loss DataCenter was established at Purdue University in 1954 to locate, assemble,and consolidate data from soil erosion studies throughout the UnitedStates.Pioneering the use of computers to analyze more than 11,000 plot-years ofbasic runoff and soil loss data from studies at 47 locations in 24 states,Walter Wischmeier (director of the NRSLDC) and collaborators developedthe Universal Soil Loss Equation (USLE) in the late 1950s. By the 1970s,the USLE (first introduced in 1958) was widely used for conservationplanning worldwide.Lots of good science went into developing the USLE
  33. 33. History of the Universal Soil Loss Equation (USLE)During the 1940s and 50s, soil scientists in the Corn Belt region began todevelop quantitative methods of predicting soil loss. It was recognized thata soil loss equation would be a valuable tool for farm planning. In 1946, aA = R * K * LS * C * Pgroup of erosion specialists held a workshop in Ohio to reappraise thefactors previously used to predict erosion (slope and management) andadded a rainfall intensity factor. The National Runoff and Soil Loss Data Rainfall erosivity factor Soil erodibility factor Topgraphy factor Cover factor Erosion control practices factor Predicted soil loss (tons/acre)Center was established at Purdue University in 1954 to locate, assemble,and consolidate data from soil erosion studies throughout the UnitedStates.Pioneering the use of computers to analyze more than 11,000 plot-years ofbasic runoff and soil loss data from studies at 47 locations in 24 states,Walter Wischmeier (director of the NRSLDC) and collaborators developedthe Universal Soil Loss Equation (USLE) in the late 1950s. By the 1970s,the USLE (first introduced in 1958) was widely used for conservationplanning worldwide.
  34. 34. Newer versions of the USLE, (RUSLE (Revised Universal Soil Loss Equation) and RUSLE 2) have been developed and are now in use by the National Resources Conservation Service (NRCS) for program planning and implementation. Major changes to the USLE incorporated into RUSLE(2) include: new and improved isoerodent maps and erodibility index (EI) distributionsfor some areas new soil erodibility factors which reflect freeze-thaw in some geographicareas new equations to account for slope length and steepness additional sub-factors for evaluating the cover and management factor forcropland and rangeland includes new conservation practice values for cropland and rangeland.A new Agriculture Handbook (No. 703) which describes RUSLE in great detail was published in 1997 and is now accessible on-line.
  35. 35. R values in ILIsoerodent lines
  36. 36. K values vary with texture and OM
  37. 37. LS factors
  38. 38. Impact of management (C and P factors)
  39. 39. The main reason why RUSLE #s do notmatch up very well with real measurements is because most erosion occurs during extreme weather events (that are not included in the RUSLE model).
  40. 40. Extreme soil erosion occurred in IA during the first 2 weeks of June 2008
  41. 41. Direct measurements of erosion are the most accurate method of quantifying soil erosion, but are also the most laborious, time consuming, and expensive. They involve collecting deposited materials and taking volumetric and weight measurements.
  42. 42. Indirect measurements of erosion use natural benchmarks and established benchmarks to evaluate long term changes in soil depth/elevation. 1) A-horizon reconstruction is the comparison of A-horizon thicknesses betweenlands suspected of being eroded and surrounding tracks of otherwise similar soil butthat are known not to have been affected by human action. 2) Natural benchmarks such as trees or boulders might have soil marks, not unlikethe high water marks on buildings in recently flooded areas. Volumeticremeasurements can be estimated on the basis of the distance between the surfaceand the mark.3) Erosion pins are metal rods set into the ground, typically with a portion sticking upabove the surface some known and recorded amount (10 cm). Flagging is tied to thestake to warn possible disturbers. The distance between the top of the pin and thesurface are recorded over time. A variation on this theme is to use a very long spikedriven through a washer to ground level. Over time, the distance the washer dropsfrom the top of the spike to the eroded ground surface can be recorded.4) Erosion pipes are similar to pins except that soil remains undisturbed within thepipe while it erodes away on the outside. Differences between soil height inside andoutside of the pipe can be compared over time.
  43. 43. The economics of off-site erosion Karl L. Guntermann, Ming T. Lee and Earl R. Swanson - 1976 Erosion and sedimentation in agriculture has traditionally been thought to result in substantial costs to the producer implying that voluntary measures at soil conservation would be in the individuals and societysinterest. The research reported here indicates that off- site sediment damages are far greater than the on- site productivity effects of erosion and that there isconsiderable justification for stronger public policies in this area. The development of the efficient production frontier reveals that conventional production techniques are quite inefficient compared to procedures that could be adopted.
  44. 44. (Pimental et al., 1995)
  45. 45. The U. S. Army Corps of Engineers spends ~ $ 100 million a year dredging the main channel of the Mississippi.
  46. 46. The U. S. Army Corps of Engineers spends ~ $ 100 million a year dredging the main channel of the Mississippi. Dustpan dredge Cutterhead dredge
  47. 47. On-site effects of erosion The main on-site impacts of accelerated erosion are loss of soil fertility and water-holding capacity. Eroded sediment normally contains elevated levels of nutrients and SOM relative to the soil left behind. Also, because the finest constituents of sediment tend to betransported furthest, eroded soils become preferentially depleted of their finer constituents over time; which often reduces their water-holding capacity. In other words, ―Erosion removes the cream of the soil‖.In affluent areas of the world, accelerated erosion’s on- site effects can often be mitigated by increased use offertilizer and irrigation; however this is not an option for much of the earth’s population.
  48. 48. What are the on-site costs of this erosion?
  49. 49. Hill-top erosion on Midwest farms
  50. 50. Tillage erosionTillage erosion has only recently been recognized as a form of soil erosion.Studies across North America and Europe have concluded that tillageerosion is the primary cause of the severe soil loss and crop yield lossobserved on hilltops.Tillage erosion is the progressive downslope movement of soil by tillagecausing soil loss on hilltops (knolls) and soil accumulation at the base ofslopes (depressions). Large, aggressive tillage implements, operated atexcessive depths and speeds are more erosive, with more passes resultingin more erosion. Landscapes that are very topographically complex (withmany short, steep, diverging slopes) are more susceptible to tillage erosion.
  51. 51. Visual evidence of tillage erosion includes loss of topsoil and exposure of subsoil at the summit of ridges and knolls; andundercutting of field boundaries, such as fence lines, on the downslope side and burial on the upslope side. The soil loss on hilltops resulting from tillage erosion reduces crop productivity and increases field variability. Rates of soil loss on hilltops are often more than 10 times what is considered to be tolerable for sustainable production. Consequently, yield losses associated with these areas are often as high as 30 to 50%.
  52. 52.
  53. 53. Moving topsoil from deposition areas to degraded areas on the Mitchell Farm in Waterloo, IA Light green zones haveexcess topsoil. Darker greenzones have successively less topsoil and red zones have the smallest amount oftopsoil. Black lines represent optimal routes for a tractorto follow when redistributing top soil. The map on the right is the expected outcome.
  54. 54. Hugh Hammond Bennett From “Soil Erosion: A National Menace (1928) “What would be the feeling of this Nation should a foreign nation suddenly enter the United States and destroy 90,000 acres of land, as erosion has been allowed to do in a single county?” “To visualize the full enormity of land impairment and devastation brought about by this ruthless agent is beyond the possibility of the mind. An era of land wreckage destined to weigh heavily upon the welfare of the next generation is at hand.”Soil scientist and showman
  55. 55. Dust from the High Plains blotted out the sun inWashington DC and helped HH Bennett convinceCongress to fund the SCS.
  56. 56. On September 13, 1933, the Soil Erosion Service wasformed in the Department of the Interior, with Bennett as chief. The service was transferred to the Department of Agriculture on March 23, 1935, and was shortly thereafter combined with other USDA units to form the Soil Conservation Service (SCS) by the Soil Conservation and Domestic Allotment Act of 1935. Hugh Bennett continued as chief, a position he held until his retirement in 1951. On October 20, 1994, the agency was renamed theNatural Resources Conservation Service (NRCS) to reflect its broader mission.
  57. 57. Hugh Hammond Bennett inspecting strip cropping in the Coon Creek Watershed – the nation’s first watershed demonstration project
  58. 58. The ~ 500 Coon Creek farmers who signed five-year contractsreceived $0.50/acre payments, foreshadowing future financialassistance programs designed to promote wise stewardship of natural resources. The Soil Conservation Service supplied Coon Creek farmerswith seed, fertilizer and fencing, and the Civilian Conservation Corps (known as the ―CCC Boys) provided a huge amount oflabor. They quarried and crushed millions of tons of limestone, installed nearly 29,000 miles of terracing, cultivated and planted many millions of trees and cleared channels and reservoirs of nearly 400,000 square yards of sediment and debris, in addition to other back-breaking tasks.
  59. 59. Coon Creek Watershed todayMore than 95% of the 92,000-acre watershed is currently covered by aconservation plan. Some current landowners still adhere to agreements their parents worked out with Bennett’s team more than 70 years ago.
  60. 60. So what has been the long term impact of the Coon Creekproject that Aldo Leopold once called an ―adventure incooperative conservation?‖Going by the numbers, a satisfying portrait emerges:•Erosion within the watershed has decreased 75%•Sediment leaving the watershed has decreased 94%•Gullies—some described as ―big enough to hold a house‖—were reduced by 77% by the late 1970s.•Flooding, once common on area farms, has been minimized.•The watershed is now 44% forested
  61. 61. Since 1936,~ $300 billion has been spent on conservation programs !
  62. 62. In the 1985 Farm Bill, Congress decided that as a quid proquo for federal farm assistance, farmers receiving taxpayersupport should control soil erosion on highly erodible lands (HEL) used to grow subsidized crops. The policy principle was straightforward and widely embraced in conservation and agriculture policy circles: taxpayer support for agriculture should not inadvertently subsidize degradation of natural resources or the environment. Parallel policies were authorized in the 1985 law to prevent subsidies from encouraging conversion of fragile lands and wetlands to crop production.
  63. 63. WHAT IS HEL LAND?According to the USDA, a field is designated as highly erodible land (HEL) if:a) RKLS/T for the soil mapping units equals or exceeds 8. b) the highly erodible soil mapping units inthe field make up 33 percent or more of the field’s acreage or c) the highly erodible soil mapping units in the field equal 50 or more acres.
  64. 64.
  65. 65. In order to maintain their eligibility for federal farm benefitssuch as commodity crop subsidies and disaster payments, farmers with subsidized crops on HEL land were required to develop and implement a government-approved soil conservation plan specifying soil conservation practices. Common erosion reduction practices include: rotating crops, minimizing tillage, leaving soil covered with crop residue after harvest, and installing grassed buffers, etc. This program was called the Highly Erodible Land Conservation (HELC) Compliance provision or ―conservation compliance‖.
  66. 66. Corn production on land classified as HEL by NRCSAcres per county 200 - 12,000 12,000 – 37,000 37,000 - 62,000 > 62,000
  67. 67. Farmers were given 10 years (until 1995) to fully implement the soil conservation plans. The U.S. Department of Agriculture (USDA) attributes the HELC planning and compliance process with widespread adoption ofconservation systems, which made unprecedented progress in reducing erosion over these 10 years. HELC compliance, coupled with the Conservation Reserve Program (CRP), reduced erosion by about 40 percent (1.2 billion tons) from 3.07 billion tons in 1982 to 1.9 billion tons in 1997 (national soil survey years which encompass the 1985 to 1995 time period). USDA attributes about 25percent of that reduction to HELC compliance requirements. HELC compliance is also credited with a ―technology- forcing‖ effect that helped reduce erosion on cropland not subject to HELC plans.
  68. 68. Since full implementation of HELC compliance plans in 1995, there has beenlittle additional progress in reducing erosion. According to the National Resources Inventory (NRI) survey, approximately 100million acres of cropland in the U.S.—nearlyone-third of the 368 million acres of cropland nationwide —continue to erode at rates deemed ―unsustainable.‖
  69. 69. Each red dot = 100,000 tons of wind erosion, total = 765 million tonsEach blue dot = 100,000 tons of water erosion, total = 960 million tons
  70. 70. HEL ComplianceIs conservation system application required on HEL ground?Yes, if the land is used to produce agricultural commodity crops.Responsibility rests with both landowners and operators to implement anappropriate conservation system or forfeit USDA program benefits.Conservation systems are specific to each HEL tract on a farm.What is the most common mistake made by operators out ofcompliance?Working soybean ground is the most common mistake that results innoncompliance. Working soybean ground even lightly can cause youroperation to be out of compliance, as many conservation systems requireno-till or strip-till on soybean stubble.Keep a few things in mind about tillage. Using aerators or rotaryharrows on fields scheduled for no-till may result in noncompliance. Striptillage with less than 25% row disturbance is equivalent to no-till. In a no-tillsystem, if ruts occur due to wet conditions at harvest, light tillage to levelthe site is acceptable, but only on the affected area. Producers shouldcontact their NRCS office before performing tillage.
  71. 71. Additional Practices Depending on your land, additional practices may berequired, such as gully and/or concentrated flow erosion control through structural practices. This may include establishment and maintenance of practices, such as: Grassed waterways Water & sediment control basins Terraces Grade control structures Diversions Other NRCS approved conservation practices
  72. 72. Is your farming system in compliance? Conservation cropping systems for HEL
  73. 73. None of the 10 Mississippi River border states reviewed sufficient numbers of tracts to achieve the one percent NRCS goal from 2000 to 2006 Number of tracts reviewed # to review each year to 2000 to State 2000 2001 2002 2003 2004 2005 2006 achieve 2006 1% review goal Arkansas 815 322 266 273 545 338 430 367 2,541 Illinois 2,883 1,184 1,162 1,030 1,061 1,803 2,257 1,977 10,474 Iowa 2,535 1,512 1,430 1,542 1,516 2,387 2,205 1,707 12,299 Kentucky 2,367 762 938 823 1,017 1,248 1,934 1,612 8,334 Louisiana 606 242 244 242 247 423 349 285 2,032 Minnesota 1,912 572 505 514 506 1,382 1,049 960 5,488 Mississippi 853 426 423 421 465 482 356 297 2,870 Missouri 1,723 838 881 1,069 922 1,283 1,103 1,185 7,281 Tennessee 1,775 361 440 440 435 584 1,059 861 4,180 Wisconsin 1,620 625 835 827 791 1,430 1,428 1,239 7,175 TOTAL 17,089 6,844 7,124 7,181 7,505 11,360 12,170 10,490 62,674
  74. 74. Erosion continues to be a serious issue in Western Illinois (#s = % of sample points) County < 1 *T 1-2*T > 2*T Adams 85 12 3 Brown 75 17 8 Hancock 91 6 3 Henderson 91 7 2 McDonough 85 12 3 Pike 70 18 11 Schuyler 83 13 4 T = tolerable level of erosion according to NRCS
  75. 75. ~ 50% of the crop acres eroding at rates > Tin the 10 Mississippi River border states are not subject to conservation compliance
  76. 76. Crop residue is not trash – its cover for the soil !!
  77. 77. This is soil pornography !
  78. 78. Photo comparison method of estimating residue cover 25% 50% 75% 90%
  79. 79. One pass with a disk~60 % residue cover
  80. 80. Two passes with a diskmight still be considered conservation tillage
  81. 81. A single disking of less abundant and more fragilesoybean residues is likely toleave less than 20% residue cover and not qualify as conservation tillage.
  82. 82. Impact of field operations onresidue cover canalso be estimatedusing tables such as the one to the right
  83. 83. Relationship between yield and residue cover
  84. 84. Line transect method of estimating residue cover
  85. 85. Line transect method of estimating residue coverThe line-transect method is an easy, reliable way to determine residue cover.It involves stretching a 50-foot measuring tape, line or rope (knotted, beadedor otherwise marked at six inch intervals) diagonally across crop rows.Percent cover is determined by counting the number of marks that intersector lie directly over a piece of residue.The key to accuracy with this method is avoiding over- or underestimation.Look straight down on each mark and take all readings on the same side ofthe tape or rope, asking yourself, ―If a raindrop falls at this point, would it hitresidue or bare soil?‖ In general, residue should be 3/32 inch (roughly thesize of a healthy wheat straw) in diameter or larger. If there is any doubt atall, do not count it.At least five measurements should be taken and averaged at each site !
  86. 86. In 2006, no-till rose to33.2% of Illinois cropland,while conventional tillagedropped to 31.2% !
  87. 87. In 2006, for the firsttime, more than half of the soybeans grown in IL were planted no-till !
  88. 88. WET SPRINGS CAUSING ILLINOIS PRODUCERS TO INCREASE FALL TILLAGEWet springs the past two years have caused an increase in crop tillage,according to a new study from the Illinois Department of Agriculture.The 2011 Illinois Soil Conservation Transect Survey revealed that no-till cropproduction has fallen five percentage points since 2009.The farmers who switched production systems have not abandoned soilconservation practices entirely, however. While the use of conventional tillageincreased during this period, so did the use of mulch-till, a practice thatleaves at least 30 percent of the residue from the previous crop on theground and, much like no-till, protects soil from erosion.No-till farming still is the conservation practice of choice among Illinoisfarmers. However, the gap between it and mulch-till has narrowedconsiderably. The survey shows 21.4 percent of fields now are planted usingmulch-till, up from 20.7 percent in 2009 and 16.4 percent in 2006. No-tillusage has declined during the same span from a record-high of 33.2 percentin 2006 to the current 24.2 percent.
  89. 89. Criteria used to rate soil suitability for no-till in PAFactors More suitable Less suitableTemperature regime Warmer: > 2800 GDD Cooler: < 2800 GDDSoil drainage Good: Most soils are well or Poor: Most soils are moderately well drained very poorly, poorly or somewhat poorly drainedWater holding Low: < 6‖ High: > 6 ―capacity of root zoneSlope High: > 8 % slope Low: < 8% slopeRock fragment High: Most soils are loamy Low: Most soils are notcontent and sandy skeletal skeletal Duiker et al., 2001
  90. 90. No-till is much more challenging on some soils butinnovative farmers are making no-till work on most soils
  91. 91. Conservation tillage is just one piece of acomprehensive approach to soil and water conservation
  92. 92. Contour strip cropping
  93. 93. Contour terraces capture sediment and transform long slopes into a series of shorter slopes.
  94. 94. Grassed waterways
  95. 95. SteveNebel Cover crops
  96. 96. Grassed filterstrip
  97. 97. Grade stabilization structure
  98. 98. Tile Drainage - it is well established through bothscientific investigation and farmer observations that improved drainage reduces surface runoff and transport of sediment.
  99. 99. Impact of the 2008 floods on IA soils 20 tons per acre average soil loss across 2,284,000 ac! Conservation structures needing repair 12,157 Grassed Waterways 8,137 Terraces 3,375 Water and Sediment Control Basins 800 Grade Stabilization Structures Fields with combinations of two or more conservation practices (e.g., no-till + covercrops) performed much better than fields with a single practice
  100. 100. Erosion is more than anagricultural issue
  101. 101. Major efforts are being made to control erosionin urban areas
  102. 102. Silt fences are intended to trap sediment while allowing water to slowly flow through.The bottom of the fabric should be buried at least six inches under the soil to preventsediment from escaping under the fence
  103. 103. Sediment retention pond
  104. 104. Diversion of water from trails prevents washouts
  105. 105. Waterway stabilized with rock and geotextile
  106. 106. Wind erosion is a serious problem in the Western US
  107. 107. Wind Erosion Equation (WEQ) E=f(IKCLV)E is the estimation of average annual soil loss in tons per acref indicates the equation includes complex relationships rather thanjust multiplication as in the USLE/RUSLE.I is the soil erodibility index.K is the ridge roughness factor.C is the climatic factor. All climatic factor values are expressed as apercentage of the value established at Garden City, Kansas.L is the unsheltered distance across an erodible field, measuredalong the prevailing wind erosion direction.V is the vegetative cover factor.
  108. 108.
  109. 109. Lots of discussion about duststorms on Ag Talk recently:―I want to say it doesnt look thatbad, but I know every pic Ivetaken "doesnt look that bad."This is definitely the worst Iveever seen. Even no-tilled groundis blowing on top of the hills.‖