Introduction to Soil Science

Introduction to Soil Science By: Sheldon Hann Soil and Land Resource Technician Agriculture and Agri-Food Canada Email: hanns@agr.gc.ca

Outline • Importance of Soil • Function of Soil • Soil Forming Factors • Soil Forming Processes • Soil Properties • Soil Horizons • Soil Drainage • Alternate/Renewable Energy and Soil

Soil Not Dirt Soil: The top layer of the earth’s surface, containing unconsolidated rock and mineral particles mixed with organic material. Dirt: Misplaced soil.

Importance “Soil is the essence of life.” • Most life on earth depends upon the soil as a direct or indirect source of food, water and shelter. • Soil is home to billions of organisms. (1ha of land ~ 25 million insects and 1million earthworms) • Soil takes 1000’s of years to develop and is destroyed easily, so it must be conserved in order to continue to support life. • 10mm of soil takes between 100 to 1000 years to form.

Function The function of soil includes: • A medium for plant growth. • A regulator of water supply. • Habitat for organisms. • A recycler of wastes. • Support of structures

Function Medium for plant growth: • Soil is a source of macro and micronutrients. • Macronutrients include nitrogen, phosphorous, potassium, nitrogen, etc. • Micronutrients include iron, manganese, zinc, copper, etc. • Soil is a source of water and nutrients for plants during the growing season. • Soil anchors plants, which increases the stability of the soil.

Function Regulate water supply: • Soil plays a vital role in cycling freshwater. • Soil filters and regulates the water supply by storing water after a precipitation event. • This stored water can then be released during the growing season, to minimize drought.

Function Habitat for organisms: • Soil is composed of billions of organisms. • These organisms decompose organic matter and convert minerals and nutrients into forms that are available to plants and animals.

Function Recycle wastes: • Soil has the ability to recycle natural wastes, if these wastes are added in appropriate amounts. • Plant residues and manure can be added to soil which will enrich nutrient concentrations and may improve soil properties.

Function Support for structures: • Soil is used for structures such as roads, causeways and as the foundation for buildings and bridges. • Soil is used for the establishment of forestry and agriculture crops.

Parent Material Soil Organisms Vegetation Topography Time Climate Soil Forming Factors The soil forming factors include: Soil Formation

Soil Forming Factors Climate: • Temperature and precipitation control the rate of weathering. • In arctic and desert areas soils develop more slowly than in hot, wet climates.

Soil Forming Factors Vegetation: • The type of vegetation influences the type and amount of organic material that is added to the soil. • Organic additions in a prairie ecosystem will be in the form of grass roots. • Organic additions in a boreal forest will be in the form of fallen plants, needles and leaves.

Soil Forming Factors Parent Material: • Soil is highly dependant on the existing parent material. • Some parent materials will weather more readily than others. • Soil developed on sandy material differs from soil developed on clay deposits.

Soil Forming Factors Soil Organisms: • Soil organisms control decomposition rates and nutrient cycling. • Bacteria, fungi and microbiota convert organic substances into soil. • Earthworms increase aeration and change the structure of the soil.

Soil Forming Factors Topography: • The physical shape of the landscape determines how much soil material is relocated by water, wind and gravity. • Topography also determines the patterns of the relocated soil.

Soil Forming Factors Time: • Soils are dynamic, continuously changing overtime. • The development of soil takes hundreds of years, therefore the time that has elapsed is an important factor. • The longer the time a soil has been forming, the more highly developed that soil will be.

Soil Forming Processes The soil forming processes include: • Chemical weathering • Physical weathering • Biological weathering

Soil Forming Processes Chemical weathering: • Caused by the chemical action of water, oxygen, carbon dioxide and organic acids. • An examples of chemical weathering is oxidation.

Soil Forming Processes Physical weathering: • Also known as “disintegration”, whereby the size of rock and soil particles are reduced without changing the chemical make-up of the particles. • An example of physical weathering would be frost wedging.

Soil Forming Processes Biological weathering: • Organisms can assist in the breakdown and formation of sediment and soil. • Examples of biological weathering are: • Root weathering • Organic weathering

Soil Properties Soil properties include: • Texture • Organic matter • Color • Structure • Consistence • Cation exchange capacity • pH

Soil Properties Texture: • Refers to the proportions of sand, silt and clay found in a given soil. • Different combinations of sand, silt and clay give rise to soil texture classes.

Soil Properties Texture Classes: * Loam is a soil that has an even mixture of sand, silt and clay. Coarse Fine

Soil Properties Organic Matter: • Increases the soil’s ability to hold water and nutrients. • Affects pore size and helps control the flow of water and air into the soil. • Generally organic matter content in soil decreases with soil depth. • Productivity increases as organic matter within the soil increases.

Soil Properties Color: • Can be used to understand parent material of the soil, the soil drainage, amount of iron and organic matter in soil. • Soils that come from siltstones have a olive-gray color and those that come from sandstones have a yellowish-brown color. • Generally soils with good drainage have bright colors. • Dark brown or black colors suggest high levels of organic matter. • Soil color is described by using the Munsell color charts.

Soil Properties Structure: • Structure influences the movement of water and gas through soils. • Soil particles that are held together by chemical and physical forces are called “peds”. • The types of soil peds define soil structure. • Structure is classified by describing: • Distinctiveness – structure of peds. • Size – size of peds. • Shape – shape of peds.

Soil Properties Consistence: • Relates to soil strength, the resistance of the soil to breaking. • Influences soil aeration and water movement through the soil and how the soil will respond to surface traffic and root penetration. • By crushing a soil ped in your hand soil consistence can be determined.

Soil Properties Consistence: The classes of consistence for moist soil are:

Soil Properties Cation exchange capacity (CEC): • A measurement of a soil’s ability to attract and hold positively charged ions (cations) at a given pH. • Determined by the amount and type of clay and organic material that is present in the soil. • Some examples of the major nutrients that are held in soil by CEC are: • Calcium • Magnesium • Iron • Potassium

Soil Properties Cation exchange capacity (CEC): • The more clay particles and organic materials found in the soil, the higher the CEC. • Soils with high CEC are better at holding soil nutrients. • Soils with low CEC tend to be less fertile then soils with high CEC, because of nutrient holding capacity.

Soil Properties pH: • A measure of the acidity or alkalinity of soil and is measured in pH units. • pH scale goes from 0 (acidic) to 14 (basic) with pH 7 as the neutral point. • Most soils have pH values between 4 and 8. • The solubility of minerals and nutrients in soil is highly dependent on the pH of that soil.

Soil Properties pH: • pH can also influence plant growth by affecting the activity of soil microorganisms. • Bacteria that decompose organic matter are hindered in strongly acidic or strongly basic soils. • This can result in a build-up of organic matter and decrease soil fertility.

Soil Horizons Soil Horizons: • Soil may consist of five horizons: • Forest floor • A horizon – zone of loss. • B horizon – zone of accumulation • C horizon – relatively unaltered parent material • R - bedrock Forest floor A B C

Soil Horizons Soil Horizons – Forest floor: • The forest floor consists of: • L (Litter layer) – Found on the ground surface and is composed of needles, leaves, twigs and other organic materials. • F (Fermented layer) – Partially decomposed organic materials such as needles, leaves and twigs. • H (Humus layer) – Fully decomposed organic material, often black-brown to nearly black in color.

Ah Ae Soil Horizons Soil Horizons – A horizon: • Due to biological activity, organic matter has accumulated in this horizon resulting in a Ah layer. • Horizon that is identifiable by the absence of clay, iron, aluminum and organic matter, resulting in a Ae layer

Soil Horizons Soil Horizons – B horizon: • Can be characterized by one or more of the following: • Enriched with clay, iron, aluminum or humus, resulting in a Bf layer. • An alteration by hydrolysis, reduction or oxidation to give a change in color or structure from above or below. Resulting in a Bm layer. Bf BC

Soil Horizons Soil Horizons – C horizon: • Can be characterized as parent material, relatively unaffected by the soil forming processes. C

Soil Drainage • Drainage is defined by the length of time it takes water to be removed from the soil in relation to the supply. • Drainage is affected by: • Soil-External Factors • Soil-Internal Factors

Soil Drainage External Factors • Position on the slope – soils in upper positions tend to be better drained than those in the lower slopes. • Aspect – Southern aspects are warmer than northern aspects, therefore southern aspects will have less soil water and better drainage. • Climate – Areas that receive high amounts of rainfall will have poorer drainage than those that receive low amounts. • Bedrock – The presence and type of bedrock can affect the rate and the flow direction of soil water.

Soil Drainage Internal Factors • Soil texture – Coarse to medium textured soils will tend to have better drainage. • Stoniness – Soils with gravels and cobbles have a improved drainage. • Consistence – Soils with loose and friable consistence will have better drainage than those with firm and very firm consistence.

Soil Drainage • Imperfectly • Poorly • Very Poorly Drainage Classes • Six classes: • Rapidly • Well • Moderately Well • Soils with good drainage tend to have bright colors. • Soils with poor drainage tend to have a grayish color.

Alternate / Renewable Energy • Soil is important for the production of alternate / renewable energy sources. • Some examples of alternate/renewable energy sources are as follows: • Biomass Energy • Wind Energy • Geothermal Energy

Alternate / Renewable Energy Biomass Energy • Soil provides the minerals and nutrients to the crops that produce biomass energy. • Biomass is solar energy stored as organic matter. • Examples of biomass energy are: • Tree and grass crops – firewood and switchgrass are two sources of renewable energy that can be easily managed. • Forestry, agricultural and urban wastes – such as residual plant waste and manure can be used as a energy source.

Alternate / Renewable Energy Wind Energy • Soil provides the foundation and anchoring for the wind turbines that produce wind energy. • Extensive planning must be done prior to the establishment of wind energy stations to minimize the risk of soil erosion. • Recognizing the areas that have soil textures and structures that may increase soil erosion and therefore be unsuitable for wind energy stations is very important.

Alternate / Renewable Energy Geothermal Energy • The temperature of the soil stays relatively constant all year round (7-14 degrees C depending on location). • Geothermal heat pumps and ground loops can be used to capture this consistent temperature and distribute it to buildings. • This system can be used for both the purposes of heating and cooling.

Thank youQuestions?

Introduction to Soil Science