Environmental Science: Toward a Sustainable Future Richard T. Wright

Environmental Science: Toward a Sustainable Future Richard T. Wright

Soil: Foundation for Land Ecosystems

PPT by Clark E. Adams

Chapter 8

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

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.

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

Topsoil Formation

Soil Profile

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

SmallSmaller

Soil Texture

Soil Texture and Properties (see Table 8-2)

Texture Water Infiltration

Water-holding Capacity

Nutrient-holding Capacity

Aeration

Sand Good Poor Poor Good

Silt Medium Medium Medium Medium

Clay Poor Good Good Poor

Loam Medium Medium Medium Medium

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

Soil Classes

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

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

The Soil Community

Humus

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

Erosion Drylands and desertification Irrigation and salinization

The Results of Removal of Topsoil: Sand and Gravel

The Importance of Humus to Topsoil

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

Dry lands and Desertification: Formation of Desert Pavement

Causes of Soil Degradation

Contour Farming and Shelterbelts

A Global View of Soil Degradation

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: What It Looks Like

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

End of Chapter 8