1. Soils!

2. 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.

3. Soil Formation
Takes 10’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.

4. Immature soil
Young soil
Mature soil

5. 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.

7. 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 –
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.

8. 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.

9. 5. Time – Development and destruction of soil profiles
Typical reaction rates are slow, the longer a rock unit has been exposed, the more likely it is to be weathered.

10. 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.
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.

11. 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: