Soils!
Soil
• Soil links the rock cycle to the biosphere (all living
things on earth).
– A mix of geologic (inorganic material) and organic
components.
• Soil Functions:
– A medium for plant growth
– Filters chemical compounds, nutrients and pollutants and
then releases them into plants, atmosphere and
organisms.
– Provides a habitat for living organisms.
– Filters water (from water cycle) into rivers, streams, lakes,
oceans, seas and ground water.
Soil Formation
• Takes 100’s – 1000’s of years to form soil (think
succession)
• Formations results from physical and chemical
weathering of rocks (rock cycle) and the gradual
accumulation of detritus (dead and decaying
materials).
– Immature soil => very low to no organic material and
very high rock material.
– Young soil => low organic material and high rock
material.
– Mature soil => high organic material, sometimes
nutrient poor.
Immature soil
Young soil
Mature soil
Soil Formation
• Horizons: The layers of soil are broken into sections called
horizons.
– O horizon – top most layer, made of newly organic materials,
grass roots, shallow plant roots ie leaf litter.
– A horizon – second layer or upper layer, mix of minerals and
decomposing organic material, plant roots, tree roots.
– E horizon – layer seen in older soils where minerals and organic
material has been leached out. Pale in color and made of mostly
silica particles.
– B horizon – layer of soluble minerals and organic matter. Clay
and iron deposits from layer above.
– C horizon – weathered rock layer.
– R horizon – Bedrock or parent material soil is composed from.
• Not all soils will contain all layers A, B, C. Most have 1-2.
Soil Types
Determining Soil Type
• 5 factors that determine soil type:
– 1. Parent material – types of inorganic materials (rocks)
that will determine how nutrient/mineral poor or healthy
the soil will be. Also will determine the thickness and
construction of soil, ie clay or sand based.
– 2. Climate –
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Temperature and precipitation
Indirect controls (e.g., types of plants)
Weathering rates
The greater the rainfall amount, the more rapid the rate
of both weathering and erosion.
– 3. Topography – depth, slope of area
– 4. Organisms – type of organisms, detritus
• Types of native vegetation
• Weathering is dependent of plant growth
• Plant and animal activity produces humic acids
that are powerful weathering agents.
• Plants can physically as well as chemically break
down rocks.
• Plants stabilize soil profiles, Animals (including
humans) tend to increase erosion.
• 5. Time –
• Development and destruction of soil
profiles
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Typical reaction rates are slow, the longer
a rock unit has been exposed, the more
likely it is to be weathered.
Soil Types
• Soil Texture: determined by the proportion of each
particle present in the soil.
– Determines the soil’s fertility and primary productivity.
• The three main types of soil are:
• Sandy
• Silt
• Clay
– Most soils are a mixture of these three, and come from the
portion of minerals found in the soil.
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Sandy soils are gritty and fall apart easily.
Silty soils feel slippery and hold together better than sandy soils.
Clay soils feel sticky and roll easily into a ball.
When each are mixed in equal proportion, the soil is considered to
be loam soil.
– Loam soil is fairly fertile and drains well. Used for agriculture.
Nutrients
Two types of nutrients – macronutrients and micronutrients
Plant need nutrients to grow and survive. They get these
nutrients from the soil.
The 3 main types of macronutrients plants use are Nitrogen,
Phosphorous, and Potassium.
These elements are considered nutrients when they are
soluble and found in compound form.
Macronutrients are usually found in short supply and can limit
productivity of agricultural crops. That is why farms and
crop growers use fertilizer to increase productivity.
Types of fertilizers: