9 Ag

 Soils

Glossary

• inorganic particles: particles that did not originate in living things.
• organic matter: matter that has come from living organisms.
• pores: the space between soil particles. Pores usually contain air or water.
• humus: a stable part of the soil formed from the breakdown of organic matter.
• weathering: the breakdown of rock to form minerals (inorganic particles) in the soil.
• parent material: the rock beneath the subsoil that weathers to become soil.
• topography: the shape and slope of the Earth's surface.
• aggregate (ped): the unit of soil structure.

Soil Formation

Copy the picture into your book - the labels and particle sizes are the important parts

Five factors control weathering and the type of soil that is formed:

• Climate
• Living organisms
• Time
• Parent material
• Topography

Soil Profile

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Soil Characteristics

Texture

Property	Sandy soil	Loamy soil	Clay soil
Particle size	Large	Medium	Fine
Pore spaces	Large	Medium	Very small
Permeability	Very good	Average	Very little
Drainage rate	Fast	Average	Slow
Ability to hold nutrients	Poor	Good	Excellent

Structure

Copy the picture into your book - the shapes of the aggregates are the important part

• Good soil structure has enough pores to allow air and water to enter and drain, but also hold water.
• Large peds help to resist erosion.
• Poor structure makes it hard for machinery and plants to penetrate.

Structure can be improved by:

• Deep ripping of compacted layers
• Reducing tillage, especially when soil is wet
• Appropriate stocking rates
• More organic matter such as stubble, green manure, and maintaining plant cover.

Soil pH

• pH measures acidity and alkalinity.
• The ability of a plant to absorb nutrients is affected by pH.