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