Foundation for Land Ecosystems Soils Foundation for Land Ecosystems

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. Sand Silt Clay Large Small Smaller

Soil Texture and Properties (see Table 8-2) Water Infiltration Water-holding Capacity Nutrient-holding Capacity Aeration Sand Good Poor Silt Medium Clay Loam

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 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

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

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 Center-pivot irrigation Irrigated lands 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