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Environmental Science: Toward a Sustainable Future Richard T. Wright

Environmental Science: Toward a Sustainable Future Richard T. Wright. Chapter 8. Soil: Foundation for Land Ecosystems PPT by Clark E. Adams. Global Trend: Where Did All the Farms Go?. Poor farming practices = loss of soils and farmland Erosion Salinization

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Environmental Science: Toward a Sustainable Future Richard T. Wright

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  1. Environmental Science: Toward a Sustainable Future Richard T. Wright Chapter 8 Soil: Foundation for Land Ecosystems PPT by Clark E. Adams

  2. Global Trend: Where Did All the Farms Go? • Poor farming practices = loss of soils and farmland • Erosion • Salinization • Development in United States = loss of 1.4 million acres of farmland per year

  3. Why a Study of Soil Is Important • 90% of the world’s food comes from land-based agriculture. • Maintenance of soil is the cornerstone of sustainable civilizations. • Simply stated, it is the “foundation” of terrestrial life.

  4. Soil: Foundation for Land Ecosystems • Soil and plants • Soil degradation • Conserving the soil

  5. Soil and Plants • Soil characteristics • Soil and plant growth • The soil community

  6. Topsoil Formation

  7. Soil Profile

  8. Soil Texture • Soil texture refers to the percentage of each type of particle found in the soil. • Loam soil is approximately 40% sand, 40% silt, and 20% clay.

  9. Soil Texture • Sand • Silt • Clay Large Small Smaller

  10. Soil Texture

  11. Soil Texture and Properties (see Table 8-2)

  12. Soil Classes • Mollisols: fertile soils with deep A horizon; best agriculture soils • Oxisols: iron and aluminum oxides in B horizon; little O horizon; poor agriculture soils

  13. Soil Classes • Alfisols: well-developed O, A, E, and B horizons; suitable for agriculture if supplemented • Aridisols: little vertical structure; thin and unsuitable for sustainable agriculture

  14. Water Transport by Transpiration

  15. Plant–Soil–Water Relationships

  16. Productive Soil • Good supply of nutrients and nutrient-holding capacity • Infiltration, good water-holding capacity, resists evaporative water loss • Porous structure for aeration • Near-neutral pH • Low salt content

  17. The Soil Community

  18. Humus • Partly decomposed organic matter • High capacity for holding water and nutrients • Typically found in O horizon

  19. Formation of Humus

  20. Humus and Development of Soil Structure

  21. Soil Degradation • Erosion • Drylands and desertification • Irrigation and salinization

  22. The Results of Removal of Topsoil: Sand and Gravel

  23. The Importance of Humus to Topsoil

  24. Erosion: Wind or Water • Splash erosion: impact of falling raindrops breaks up the clumpy structure of topsoil • Sheet erosion: running water carries off the fine particles on the soil surface • Gully erosion: water volume and velocity carries away large quantities of soil, causing gullies (see Fig. 8-14)

  25. Desertification • Formation and expansion of degraded areas of soil and vegetation cover in arid, semiarid, and seasonally dry areas, caused by climatic variations and human activities.

  26. Dryland Areas • Cover one-third of Earth’s land area • Defined by precipitation, not temperature • United Nations Convention to Combat Desertification (UNCCD) • Fund projects to reverse land degradation • In 2003, $500 million available in grants to fund projects

  27. Dry lands and Desertification: Formation of Desert Pavement

  28. Causes of Soil Degradation

  29. Contour Farming and Shelterbelts

  30. A Global View of Soil Degradation

  31. Irrigation • Flood irrigation (see Fig. 8-21) • Center-pivot irrigation (see Fig. 7-16) • Can extract as much as 10,000 gallons/minute • Irrigated lands • 67 million acres or one-fifth of all cultivated cropland in the United States • 667 million acres worldwide, a 35% increase over the past 30 years

  32. Salinization: What It Looks Like

  33. Salinization • A process of distilling out dissolved salts in irrigated water and leaving it on the land • A form of desertification, since land is rendered useless • Worldwide an estimated 3.7 million acres of agricultural land is lost annually to salinization and waterlogging

  34. Conserving the Soil • Cover the soil • Minimal or zero tillage • Mulch for nutrients • Maximize biomass production • Maximize biodiversity

  35. End of Chapter 8

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