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Unit 13: Soil Erosion Chapter 11. Objectives  How soil erosion affects your life  Magnitude of the soil erosion problem  Causes & methods of soil erosion.

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Presentation on theme: "Unit 13: Soil Erosion Chapter 11. Objectives  How soil erosion affects your life  Magnitude of the soil erosion problem  Causes & methods of soil erosion."— Presentation transcript:

1 Unit 13: Soil Erosion Chapter 11

2 Objectives  How soil erosion affects your life  Magnitude of the soil erosion problem  Causes & methods of soil erosion  Controlling erosion

3 Introduction  North America’s most devastating environmental disaster Much topsoil lost resulting in greatly decreased production capability Plugs channels & raises riverbeds, increasing flood risks  Geologic Soil Erosion – natural wearing away of land surface by water, wind, or ice Not addressed here  We’ll address erosion related to human activity

4 The Soil Erosion Problem  Erosion problem two-fold Lost productivity Sediment pollution  Exposed B horizons, much less productive 9-18% corn yield reductions 17-24% SB yield reductions  Al toxicity risks much higher

5 The Soil Erosion Problem  Sediment Major carrier of pesticides & fertilizer that pollutes the ecosystem where it settles Also make lakes, rivers more shallow  Ex. Eastern Washington – in last century, 40% of topsoil has eroded  Much focus on stream bank erosion, erosion at construction sites (land left unprotected for extended time)

6 The Soil Erosion Problem  Minimization is the goal (elimination of erosion impossible)  Since 1935 $30 b spent to erosion control in U.S.

7 Nature of Water Erosion  Effects: destroys human-made structures; fill reservoirs, lakes, rivers; damages land Mud, silt, sediment  Eroded material usually the richest part of the soil Highest nutritive content Most organic matter

8 Nature of Water Erosion  Causes of Water Erosion Peds disintegrate w/ impact of rain drops  Soil aggregates separate  Particles can move ~5’ w/ splash erosion  Most destructive on bare soil Rainfall then moves particles w/ water flow on soil surface  Scours channels in soil surface  Each subsequent rain adds to depth/width of these channels  Form: gullies, rills

9 Nature of Water Erosion Causes: excessive tillage, burning crop residue, overgrazing, clear-cutting forests  Raindrop Splash Erosion Not as detrimental in clay soils due to strong adhesion forces  More common in fine sands, silty soils Clays more likely to crust over, decreasing aeration, slows infiltration  Water then must wash over soil surface

10 Nature of Water Erosion  Sheet & Channelized-Flow Erosion Sheet erosion – water moves an entire layer of soil Rills – water-cut channels in the soil  Can be erased by tillage Gullies – large, deep channels caused by excessive movement of water  Can’t cross w/ equipment Sheet & rill most common & problematic  Harder to detect

11 ademics/classes/soil2125/im g/erosb3.jpg

12 du/fpadmin/weppmain/overv iew/rill.html

13 /Browse/gullyero/gullyero. htm

14 Erosion Tolerance  Erosion Tolerance Level (T) – maximum rate of annual soil loss that will permit crop productivity to be maintained indefinitely Highly erodable land – reduce erosion to 5 t/ac/yr Some soils – 1-2 t/ac/yr

15 Water Erosion Control  Controlling Soil Detachment Cropping/vegetative practices the keep soil surface covered as much as possible Energy from rain drops dissipated/minimized by hitting residue first Leaving residue cover:  Not plowing under stubble  Planting a cover crop

16 Water Erosion Control  Controlling Soil Transport Slow eroding water Reduce steepness of slopes (if possible) Construct barriers or terraces  Reduces slope, appropriate for areas of high-intensity rainfall  Reduces velocity of runoff  Can be costly

17 Water Erosion Control Cultivate on the contour  Plant at right angles to natural slope  Appropriate for slopes 2-8% Strip crop  Plant on contour  Alternate row crops w/ close-growing crops  Not only slows erosion, but can filter what is eroded Filter strips  Plant on low end of field to prevent chemicals/fertilizer from entering adjacent ditches/streams  IA study – 10’ filter strip reduced sediment load 70%, 30’ strip 85%

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20 Water Erosion Control  Cover Crops – grown during off-season Legumes, cool-season grasses  Hairy vetch, clover – can also add N to soil Good cover crops should:  Increase soil organic matter  Improve water infiltration  Reduce runoff May harvest, or burn down w/ herbicide In dry areas – use is limited due to risk of depleting soil water content

21 Water Erosion Control  Erosion Control for Construction Sites Erosion can far exceed any agricultural erosion Greater effort needed to minimize erosion Construction site barren soil can erode 1 t/ac over a few storms Methods used to control erosion  Mulch  Soil binders  Logs  Blankets

22 Nature of Wind Erosion  Rates can be high on dry, bare, weak aggregate soils  Soil particles can be held in suspension and blown away  44% of erosion caused by wind  Most of our land: wind erosion risk small  Highest risk areas: TX, NM  1/3 of land surface – high risk for wind erosion

23 Nature of Wind Erosion  Arid & semiarid soils at highest risk Less vegetation, less cover Less clay, less aggregation Less soil moisture, lighter wt  Desertification – process of soil degradation by wind erosion, resulting in coarser soils, lessen ability to retain water

24 Wind-Erosion Control  Ridge-till – decreases ability of wind to blow away soil steadily across surface Reduces wind velocity Traps soil 2-4” ridges ideal  Reduce field length  Increase soil cover  Use windbreaks

25 Assignment


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