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Environmental Science: Toward a Sustainable Future Richard T. Wright. Chapter 8. Soil: Foundation for Land Ecosystems, and a very Earthy Subject. Why a Study of Soil Is Important. 90% of the world’s food comes from land-based agriculture.
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Environmental Science: Toward a Sustainable Future Richard T. Wright Chapter 8 Soil: Foundation for Land Ecosystems, and a very Earthy Subject
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 (Ecosystem Capital! No soil, you die!!!!) • Simply stated, it is the “foundation” of terrestrial life.
Soil: Foundation for Land Ecosystems • Soil and plants • Soil degradation • Conserving the soil
Soil and Plants • Soil characteristics • Soil and plant growth • The soil community
Soil Profile Leaching dissolves and brings minerals down Weathering breaks down & brings particles up
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.
Soil Texture • Sand • Silt • Clay Large Small Smaller
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
Humus • Partly decomposed organic matter • High capacity for holding water and nutrients • Typically found in O horizon
Soil Degradation • Erosion • Drylands and desertification • Irrigation and salinization
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)
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.
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
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
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
Conserving the Soil • Cover the soil • Minimal or zero tillage • Mulch for nutrients • Maximize biomass production • Maximize biodiversity
Things to know from Chapter 8:What is topsoil made from?What are the O,A,B, and C horizons?What is loam?Infiltration, water-holding capacity, aerationWhat is humus? What does it do for the soil?What is mineralization? How is soil degraded?What is the advantages and disadvantages of irrigation?What is salinization?How do we conserve soil?