1. Foundation for Land Ecosystems
Soils
Foundation for Land Ecosystems

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.
Sand
Silt
Clay
Large
Small
Smaller

9. Soil Texture and Properties (see Table 8-2)
Water Infiltration
Water-holding Capacity
Nutrient-holding Capacity
Aeration
Sand
Good
Poor
Silt
Medium
Clay
Loam

10. 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
Alfisols: well-developed O, A, E, and B horizons; suitable for agriculture if supplemented
Aridisols: little vertical structure; thin and unsuitable for sustainable agriculture

11. Water Transport by Transpiration

12. Plant–Soil–Water Relationships

13. 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

14. The Soil Community

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

16. Soil Degradation Erosion Drylands and desertification
Irrigation and salinization

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

18. The Importance of Humus to Topsoil

19. 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

20. 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.

21. 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

22. Dry lands and Desertification: Formation of Desert Pavement

23. Causes of Soil Degradation

24. Contour Farming and Shelterbelts

25. A Global View of Soil Degradation

26. Irrigation Flood irrigation Center-pivot irrigation Irrigated lands
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

27. Salinization: What It Looks Like

28. 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

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