Chapter 8:Soil

Goals• Understand how the soil quality

determines what can grow • Understand how soil quality can determine

the survival of societies

Note: Fig. 8-4 in our book also includes the “E horizon”

O Horizon• Humus- dark, soft, spongy residue of

organic matter as a result of decomposition of organic matter such as leaves and dead wood

• 1 ۫ source of nutrients in soil systems

A Horizon

• Top soil-mixture of humus and leachial mineral soil

• Thin roots extend into this layer

E Horizon• Eluviation

process of leaching (note: You may see this word spelled with and I, A, or E)

• Minerals are “leached” into this layer from H2O moving downward

• Accumulation of elluvial organic matter

• Often high in iron, aluminum, and calcium

• Often high in clay content

• Unweathered parent material

• Shows little or no sign of soil formation (primary succession)

• Glacial deposits, volcanic ash

• Reveals history of the land

Texture

Sand 2.0-.02 mmSilt .02-.002 mmClay.002mm ≥ some microscopic

Porosity and Permeability

LOAM: 40%sand 40% silt 20% clay

Loam is theoretically the ideal soil

ltpwww.gsfc.nasa.gov/ globe/pvg/texture3.htm

Classes of SoilMollisols- very fertile, dark, found in temperate grasslands, best agricultural soil, Deep A horizonOxisols- soil of tropical and subtropical rainforest layer of iron and Al oxides in B horizon, little O horizonAlfisols- weathered forest soil, not deep, but developed OAE+B typical of most temperate forest biome. Need fertilizer for agricultureAridsols- dry lands + desert, lack of vegetation, lack of rain unstructured vertically, irrigation leads to salinization because of high evaporation.

The Public Policy and Soil

Low Input sustainable Agriculture (LISA)-started by US Defense of Agriculture in 1988

Conservation Reserve Program- 1985

Food Security Act of 1985

Federal Agriculture Improvement and Reform (FAIR) 1996

Environmental Quality Incentive Program (EQUIP)

Know these Acts and Laws:

LOAM: 40%sand 40% silt 20% clay

Loam is theoretically the ideal soil

ltpwww.gsfc.nasa.gov/ globe/pvg/texture3.htm