Download Soil Erosion - Soils and Soil Supplements - Lecture Slides and more Slides Biology in PDF only on Docsity! Unit 13: Soil Erosion Docsity.com Objectives • How soil erosion affects your life • Magnitude of the soil erosion problem • Causes & methods of soil erosion • Controlling erosion Docsity.com 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) Docsity.com The Soil Erosion Problem • Minimization is the goal (elimination of erosion impossible) • Since 1935 $30 b spent to erosion control in U.S. Docsity.com 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 Docsity.com 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 Docsity.com http://www.soils.umn.edu/ac ademics/classes/soil2125/im g/erosb3.jpg Docsity.com http://topsoil.nserl.purdue.e du/fpadmin/weppmain/overv iew/rill.html Docsity.com 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 Docsity.com 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 Docsity.com 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% Docsity.com 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 Docsity.com 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 Docsity.com 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 Docsity.com
