View
66
Download
0
Category
Tags:
Preview:
DESCRIPTION
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?. Poor farming practices = loss of soils and farmland Erosion Salinization - PowerPoint PPT Presentation
Citation preview
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
Small
Smaller
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
Recommended