3. soil screwed up (great)


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3. soil screwed up (great)

  2. 2. 9/29/2013 Guru IBESS SOIL SYSTEM http://www.nbclearn.com/portal/site/learn/changing-planet Withering Crops 2
  3. 3. 9/29/2013 Guru IBESS SOIL SYSTEM 3 Bad results: Mineralization • If detritus is lost, soil organisms starve • Soil will no longer be kept loose and nutrient-rich • Humus decomposes, breaking down the clumpy aggregate structure of glued soil particles • Water- and nutrient-holding capacities, infiltration, and aeration decline • Mineralization: loss of humus and collapse of topsoil • All that remains are the minerals (sand, silt, clay) • Topsoil results from balancing detritus and humus additions and breakdown
  4. 4. 9/29/2013 Guru IBESS SOIL SYSTEM The importance of humus to topsoil 4
  5. 5. 9/29/2013 Guru IBESS SOIL SYSTEM 5 Bad results: Soil degradation • Turnover of plant material produces detritus • When humans cut forests, graze livestock, or plant crops, the soil is managed or mismanaged. • Soil degradation: occurs when key soil attributes required for plant growth or other ecosystem services deteriorate. • Some reports on soil degradation are incorrect or outdated • 75% of the land in Burkina Faso was said to be degraded • But agricultural yields have increased due to soil and water conservation
  6. 6. 9/29/2013 Guru IBESS SOIL SYSTEM 6 Bad Soil: Erosion 1. Erosion: the process of soil and humus particles being picked up and carried away by water and wind 1. Occurs any time soil is bared and exposed 2. Soil removal may be slow and gradual (e.g., by wind) or dramatic (e.g., gullies formed by a single storm) • Vegetative cover prevents erosion from water • Reducing the energy of raindrops • Allowing slow infiltration • Grass is excellent for erosion control • Vegetation also slows wind velocity
  7. 7. 9/29/2013 Guru IBESS SOIL SYSTEM Splash, sheet, and gully erosion • Splash erosion: begins the process of erosion • Raindrops break up the clumpy structure of topsoil • Dislodged particles wash between other aggregates • Decreases infiltration and aeration • Sheet erosion: the result of decreased infiltration • More water runs off, carrying away fine particles • Gully erosion: water converges into rivulets and streams • Water’s greater volume, velocity, energy remove soil • Once started, erosion can turn into a vicious cycle • Less vegetation exposes soil to more erosion 7
  8. 8. 9/29/2013 Guru IBESS SOIL SYSTEM 8 Causes of erosion: overcultivation • Plowing to grow crops exposes soil to wind and water erosion • Soil remains bare before planting and after harvest • Plowing causes splash erosion • Destroying soil’s aggregate structure • Decreasing aeration and infiltration • Tractors compact soil • Reducing aeration and infiltration • Increasing evaporative water loss and humus oxidation • Rotating cash crops with hay and clover is sustainable
  9. 9. 9/29/2013 Erosion Guru IBESS SOIL SYSTEM 9
  10. 10. 9/29/2013 Guru IBESS SOIL SYSTEM 10 The other end of the erosion problem • Water that does not infiltrate enters streams and rivers • Causing flooding • Sediment: eroded soil carried into streams and rivers • Clogs channels, intensifies floods, fills reservoirs • Kills fish and coral reefs • Damages streams, rivers, bays, estuaries • Excess sediments and nutrients from erosion are the greatest pollution problem in many areas • Groundwater is depleted • Rainfall runs off and does not refill soil or ground water
  11. 11. 9/29/2013 Guru IBESS SOIL SYSTEM 11 Desert pavement • Another devastating feature of wind and water erosion: differential removal of soil particles • Lighter humus and clay are the first to be carried away • Rocks, stones, coarse sand remain • The remaining soil becomes coarser • Deserts are sandy because wind removes fine material • Desert pavement: occurs in some deserts • Removal of fine material leaves a thin surface layer of stones and gravel • This protective layer is easily damaged (e.g., by vehicles)
  12. 12. 9/29/2013 Guru IBESS SOIL SYSTEM Formation of desert pavement 12
  13. 13. 9/29/2013 Guru IBESS SOIL SYSTEM 13 Drylands and desertification • Clay and humus are the most important parts of soil • For nutrient- and water-holding capacity • Their removal results in nutrients being removed • Regions with sparse rainfall or long dry seasons support grasses, scrub trees, and crops only if soils have good waterand nutrient-holding capacity • Erosion causes these areas to become deserts • Desertification: a permanent reduction in the productivity of arid, semiarid, and seasonally dry areas (drylands) • Does not mean advancing deserts
  14. 14. 9/29/2013 Desertification Guru IBESS SOIL SYSTEM 14
  15. 15. 9/29/2013 Guru IBESS SOIL SYSTEM 15 Drylands • Desertification is a process of land degradation • Due to droughts, overgrazing, erosion, deforestation, overcultivation • It is extremely serious because it is permanent • Dryland ecosystems cover 41% of Earth’s surface • They are defined by precipitation, not temperature • They receive minimal rainfall • Droughts are common—they can last for years • Rainfall causes vegetation to return so drylands are not desertified
  16. 16. 9/29/2013 Guru IBESS SOIL SYSTEM 16 Preventing soil degradation • Several farming strategies to prevent soil degradation: • • Crop rotation • • Contour farming • • Intercropping • • Terracing • • Shelterbelts • • Conservation tillage
  17. 17. 9/29/2013 Guru IBESS SOIL SYSTEM 17 Reducing soil erosion • Contour strip cropping: plowing and cultivating at right angles to contour slopes • Shelterbelts: protective belts of trees and shrubs planted along plowed fields • The U.S. Natural Resource Conservation Service (NRCS) • Established in response to the Dust Bowl • Regional offices provide information to farmers and others regarding soil and water conservation practices • U.S. soil erosion has decreased through conservation • Windbreaks, grassed waterways, vegetation to filter runoff
  18. 18. 9/29/2013 Guru IBESS SOIL SYSTEM 18 Recent soil conservation laws • The U.S. has continued to pass soil conservation legislation in recent years: • • Food Security Act of 1985 • • Conservation Reserve Program, 1985 • • Freedom to Farm Act, 1996 • • Low-Input Sustainable Agriculture Program, 1998 • Internationally, there is the UN’s “FAR” program in Asia.
  19. 19. 9/29/2013 Guru IBESS SOIL SYSTEM 19 Crop rotation • Alternating the crop planted (e.g., between corn and soybeans) can restore nutrients to soil and fight pests and disease. Figure 8.16a
  20. 20. 9/29/2013 Guru IBESS SOIL SYSTEM 20 Contour farming • Planting along contour lines of slopes helps reduce erosion on hillsides. Figure 8.16b
  21. 21. 9/29/2013 Guru IBESS SOIL SYSTEM 21 Intercropping • Mixing crops such as in strip cropping can provide nutrients and reduce erosion. Figure 8.16c
  22. 22. 9/29/2013 Guru IBESS SOIL SYSTEM 22 Terracing • Cutting stairsteps or terraces is the only way to farm extremely steep hillsides without causing massive erosion. It is laborintensive to create, but has been a mainstay for centuries in the Himalayas and the Andes. Figure 8.16d
  23. 23. 9/29/2013 Guru IBESS SOIL SYSTEM 23 Shelterbelts • Rows of fast-growing trees around crop plantings provide windbreaks, reducing erosion by wind. Figure 8.16e
  24. 24. 9/29/2013 Guru IBESS SOIL SYSTEM 24 Tillage • Plowing has multiple desirable effects: –Weeds and weed seeds are buried / destroyed. –Crop residue is turned under - decays faster and helps build soil structure. –Leached nutrients brought closer to surface. –Cooler, darker soil is brought to top and warmed.
  25. 25. 9/29/2013 Guru IBESS SOIL SYSTEM 25 Problem: • Each trip over the field is an added expense to the farmer, and at the same time increases the amount of time the soil is open to erosion via wind or water.
  26. 26. 9/29/2013 Guru IBESS SOIL SYSTEM 26 No-till planting • No-till agriculture: a technique allowing continuous cropping while minimizing erosion • Routinely practiced in the U.S. • After spraying a field with herbicide to kill weeds • A planting apparatus cuts a furrow through the mulch • Drops seeds and fertilizer • Closes the furrow • The waste from the previous crop becomes detritus • So the soil is never exposed • Low-till farming uses one pass (not 6–12) over a field • http://www.youtube.com/watch?v=I_7d0h2bSoY&feature =related
  27. 27. 9/29/2013 Guru IBESS Apparatus for no-till planting SOIL SYSTEM 27
  28. 28. 9/29/2013 Guru IBESS SOIL SYSTEM 28 Conservation tillage • No-till and reduced-tillage farming leaves old crop residue on the ground instead of plowing it into soil. This covers the soil, keeping it in place. • Here, corn grows up out of a “cover crop.” Figure 8.16f
  29. 29. 9/29/2013 Guru IBESS SOIL SYSTEM 29 Conservation tillage • Conservation tillage is not a panacea for all crops everywhere. • It often requires more chemical herbicides (because weeds are not plowed under). • It often requires more fertilizer (because other plants compete with crops for nutrients). • But legume cover crops can keep weeds at bay while nourishing soil, and green manures can be used as organic fertilizers.
  30. 30. Guru IBESS Trade-Offs 9/29/2013 SOIL SYSTEM Conservation Tillage Advantages Reduces erosion Saves fuel Disadvantages Can increase herbicide use for some crops Cuts costs Holds more soil water Reduces soil compaction Allows several crops per season Does not reduce crop yields Reduces CO2 release from soil Leaves stalks that can harbor crop pests and fungal diseases and increase pesticide use Requires investment in expensive equipment 30
  31. 31. 9/29/2013 Guru IBESS SOIL SYSTEM 31 Waterlogging and salinization • Overirrigation can raise the water table high enough to suffocate plant roots with waterlogging. • Salinization (buildup of salts in surface soil layers) is a more widespread problem. • Evaporation in arid areas draws water up through the soil, bringing salts with it. Irrigation causes repeated evaporation, bringing more
  32. 32. 9/29/2013 Guru IBESS SOIL SYSTEM 32 Fertilizers • Supply nutrients to crops • Inorganic fertilizers = mined or synthetically manufactured mineral supplements • Organic fertilizers = animal manure, crop residues, compost, etc. Figure 8.18
  33. 33. 9/29/2013 Guru IBESS SOIL SYSTEM 33 Global fertilizer usages • Fertilizer use has risen dramatically in the past 50 years. Figure 8.19b
  34. 34. 9/29/2013 Guru IBESS SOIL SYSTEM 34 Inorganic fertilizer • Can provide optimal amounts of nutrients efficiently • But it lacks organic matter to support organisms and build soil structure • It can keep nutrient content high under intensive cultivation (two or more cash crops/year) • But mineralization and soil degradation proceed • Additional fertilizer leaches into waterways • Chemical fertilizers have a valuable place in agriculture • Organic fertilizers may not have enough nutrients • Growers must use each fertilizer as necessary
  35. 35. 9/29/2013 Guru IBESS SOIL SYSTEM 35 Soil conservation & Sustainable Ag • Sustainability means doing all we can to reduce erosion • Soil conservation must be practiced at two levels • Individual landholders can best preserve soil through traditional knowledge and practices • Public policies can lead to conservation or disaster • Goals: • Maintain productive topsoil • Keep food safe and wholesome • Reduce chemical fertilizers and pesticides • Keep farms economically viable • Sustainable options mimic past practices • Contouring, crop rotation, terracing, little or no chemicals • The U.S. Sustainable Agriculture Research and Education program (SARE) (1988) • Provides $5–12 million/year for building and disseminating knowledge about sustainable agriculture