Environmental Science Toward a Sustainable Future Richard T
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? n Poor farming practices = loss of soils and farmland q q n Erosion Salinization Development in United States = loss of 1. 4 million acres of farmland per year
Why a Study of Soil Is Important n n n 90% of the world’s food comes from landbased agriculture. Maintenance of soil is the cornerstone of sustainable civilizations. Simply stated, it is the “foundation” of terrestrial life.
Soil: Foundation for Land Ecosystems n n n Soil and plants Soil degradation Conserving the soil
Soil and Plants n n n Soil characteristics Soil and plant growth The soil community
Topsoil Formation
Soil Profile
Soil Texture n Soil texture refers to the percentage of each type of particle found in the soil. q Loam soil is approximately 40% sand, 40% silt, and 20% clay.
Soil Texture n n n Sand Silt Clay Large Smaller
Soil Texture
Soil Texture and Properties (see Table 8 -2) Texture Water Infiltration Waterholding Capacity Nutrientholding Capacity Aeration Sand Good Poor Good Silt Medium Clay Poor Good Poor Loam Medium
Soil Classes n n Mollisols: fertile soils with deep A horizon; best agriculture soils Oxisols: iron and aluminum oxides in B horizon; little O horizon; poor agriculture soils
Soil Classes n n Alfisols: well-developed O, A, E, and B horizons; suitable for agriculture if supplemented Aridisols: little vertical structure; thin and unsuitable for sustainable agriculture
Water Transport by Transpiration
Plant–Soil–Water Relationships
Productive Soil n n n Good supply of nutrients and nutrientholding capacity Infiltration, good water-holding capacity, resists evaporative water loss Porous structure for aeration Near-neutral p. H Low salt content
The Soil Community
Humus n n n Partly decomposed organic matter High capacity for holding water and nutrients Typically found in O horizon
Formation of Humus
Humus and Development of Soil Structure
Soil Degradation n Erosion Drylands and desertification Irrigation and salinization
The Results of Removal of Topsoil: Sand Gravel
The Importance of Humus to Topsoil
Erosion: Wind or Water n n n 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)
Desertification n 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.
Dryland Areas n n n Cover one-third of Earth’s land area Defined by precipitation, not temperature United Nations Convention to Combat Desertification (UNCCD) q q Fund projects to reverse land degradation In 2003, $500 million available in grants to fund projects
Dry lands and Desertification: Formation of Desert Pavement
Causes of Soil Degradation
Contour Farming and Shelterbelts
A Global View of Soil Degradation
Irrigation n n Flood irrigation (see Fig. 8 -21) Center-pivot irrigation (see Fig. 7 -16) q n Can extract as much as 10, 000 gallons/minute Irrigated lands q q 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
Salinization: What It Looks Like
Salinization n 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
Conserving the Soil n n n Cover the soil Minimal or zero tillage Mulch for nutrients Maximize biomass production Maximize biodiversity
End of Chapter 8
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