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Unit 13: Soil Erosion Chapter 11.

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Presentation on theme: "Unit 13: Soil Erosion Chapter 11."— 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




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 Strip crop
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%



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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