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 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.

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 – • 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

• 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.• 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 micronutrientsPlant 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: