12.1 Soil Formation
Chapter 12 – Soil and Agriculture
Arable – farmable land
DIRT = bad word
SOIL – complex plant-supporting system made of disintegrating rock, remains and
wastes of organisms, water, gases, nutrients, and microorganisms.
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Renewable/sustainable
hundreds to thousands of years to renew
1 inch of topsoil
finite = limited
5 factors of soil formation
desert
rain
mountains
1. Landforms – mountains and valleys affect sun, rain and wind exposure
Steep slopes promote erosion.
2. Time – soil formation takes decades, centuries, or millennia
3. Climate – soil created faster in warm, wet weather
4. Organisms – earthworms and other burrowing animals aerate soil and
add organic matter, and speed decomposition
5. Parent material (bedrock) – the rock soil is made from has different
chemical and physical properties
12.1
soil horizons – layers of soil
soil profile – cross-section of soil from surface to bedrock
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few soils contain all of the six layers
O Horizon = Litter Layer
A Horizon = Topsoil
E Horizon = Leaching
B Horizon = Subsoil
C Horizon = Weathered Parent Material
R Horizon = Parent Material - Bedrock
topsoil – most important to humans and what we degrade
soil characteristics – color, texture, structure, pH (measurement of acidy)
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Color – darker the soil, the richer in nutrients
Texture – clay (smallest), silt, sand (largest)
Loam – mixture of each of the particles
BEST = silty or loamy
Structure – arrangement of soil particles
 BEST = clumpy
pH = affects ability for plants to grow
deposition – taking soil from one area & putting into another
o usually caused by erosion
o helps with primary succession
Humus – dark, spongy, crumbly mass of material that is high in nutrients =
ideal soil