1. Soil: Foundation for Land Ecosystems
Chapter 8
Soil: Foundation for Land Ecosystems
Copyright © 2008 Pearson Prentice Hall, Inc.

2. 8.1 - 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 Ecosystem: Distinguishing Characteristics – Part 1
Slow rate of nutrient and energy transfer
Few months: tropical rainforest
Few years: temperate forests
Different textures demand different adaptations, e.g., worms and pocket gophers
Near total reliance on decomposers

5. Soil Ecosystem: Distinguishing Characteristics – Part 2
Exclusive use of detritus for energy and nutrients
Extreme susceptibility to disturbance and slow recovery times

6. Topsoil Formation

7. Soil Formation and Nutrient Uptake
(click to view animation)
Soil Formation

8. Soil Profile

9. Soil Particles Sand - largest, can see with naked eye, 2 mm to 0.02 mm
Silt - medium, 0.02 mm to mm
Clay - very fine, smaller than mm

10. 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.

11. Soil Texture Triangle

12. Soil Formation and Nutrient Uptake
Nutrient Availability
(click to view animation)
Nutrient Availability

14. Water Transport by Transpiration

15. Plant-soil-water Relationships

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

17. The Soil Community: The 5% Organic Component

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

19. Humus and Development of Soil Structure

20. 8.2 - The Importance of Humus to Topsoil

21. GLADSOD Global assessment of soil degradation map (1987-1990)
No global data on soils existed at the time
Informal surveys (not very accurate)
Very few actual samples collected
GLADSOD estimated that desertification had occurred on 20% of the land worldwide
Current estimates closer to 10%

22. 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 (next slide)

24. 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.

25. Formation of Desert Pavement

26. Formation of Desert Pavement

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. Desertification

29. Three Major Practices That Expose Soil to Erosion
Overcultivation - planting crops/farming
Overgrazing - from livestock
Deforestation - cleared for farming or construction

30. Causes of Soil Degradation

31. Alternative Farming Practices That Conserve Soil
No-till planting - kill weeds chemically, then plant and add fertilizer
Contour farming - right angle to slope
Shelter belts - trees around fields
Dry land farming – minimize irrigation
Crop Rotation – especially legume vs. non-legume

32. Contour Farming

33. Shelterbelts

34. Irrigation Flood irrigation (next slide)
Center-pivot irrigation (Chapter 7)
Can extract as much as 10,000 gallons/minute
Irrigated lands
67 million acres or one-fifth of all cultivated crop land in the United States
667 million acres worldwide, a 35% increase over the past 30 years

35. Flood Irrigation

36. 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 are lost annually to salinization and waterlogging

37. 8.3 - Public Policy and Soils
Soil and Water Conservation Act of aid landowners and users; evaluate U.S. soils, water, and related resources
Food Security Act (1985) - “Swampbuster” - discouraged conversion of wetlands
Subsidies
Numerous Farm Bills

38. Conserving the Soil Cover the soil - cover crop
Minimal or zero tillage
Mulch for nutrients
Maximize biomass production
Maximize biodiversity