Environmental Science: Toward a Sustainable Future Richard T. Wright

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

3. 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

4. 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.

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

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

7. Topsoil Formation

8. Soil Profile

9. 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.

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

11. Soil Texture

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

13. 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

14. 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

15. Water Transport by Transpiration

16. Plant–Soil–Water Relationships

17. 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

18. The Soil Community

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

20. Formation of Humus

21. Humus and Development of Soil Structure

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

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

24. The Importance of Humus to Topsoil

25. 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)

26. 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.

27. 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

28. Dry lands and Desertification: Formation of Desert Pavement

29. Causes of Soil Degradation

30. Contour Farming and Shelterbelts

31. A Global View of Soil Degradation

32. 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

33. Salinization: What It Looks Like

34. 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

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

36. End of Chapter 8