Soil Science

SoilsAg Science

SoilI. Soil is a layer on the earth’s crust that

provides a combination of resources. Allow for the growth of plants and animals.

A. Oxygen – needed for adequate root growthB. Temperature – soil absorbs heat from the

sun. Used for plant growth and seed germination

C. Water – used for plant growthD. Carbon – utilized in the form of organic matterE. Nutrients – provided as minerals. Broken

down as nitrogen and recycled through decaying material.

II. Soil is composed of 4 different components.A. Solid Portion (50%)

1. Mineral Matter – 45% of the soil. Partially decomposed rock, ie. sand, silt, clay

2. Organic Matter - ~5% of the soil. Partially decomposed plant & animal material. Gives soil its color

B. Pore spaces (50% of the soil)1. Air – accounts for 25% of the soil. When soils are wet, less air. When soils are dry, more air.2. Water – accounts for 25% of the soil. When it rains, water either enters the soil or runs off.

Water cont.Infiltration – process of water soaking into

the soil.Once water is in the soil, the movement

downward is called percolation.A soil that allows for both is called

permeable

• Water in the soil my be one of three types– Gravitational water – water that drains through

the pore spaces (leaching occurs)– Capillary water – water that is held between

particles of soil against forces of gravity; may move upward or sideways

– Hygroscopic water – water that forms a thin film around individual soil particles; unavailable to plants.

III. Abundant life can be found in soil.A. Forms of life in the soil include:

1. Earthworms2. Insects3. Bacteria4. Fungi5. Other organisms

B. Bacteria & fungi have an important role in the soil. They breakdown o.m. and release nutrients

C. Earworms, ants, crawfish, moles, and other organisms improve the tilth, or ease at which soil can be worked.These organisms create openings in the soil as they tunnel. This helps drainage and improves gas exchange.

IV. Plants depend on soil to provide 4 basic needs.A. Anchorage – soil acts to provide a firm support

as roots grow throughout the soil.B. Water – soil provides nearly all of the water

used by plants. Water is absorbed through the plants’ roots.

C. Oxygen – nearly all organisms need oxygen. Roots don’t have ample supplies, so they need good soil aeration to allow gas exchange.

D. Nutrients – of the 16 nutrients considered to be essential for plant growth, 13 are obtained from the soil. Root hairs absorb the nutrients dissolved in soil water.

V. Ag depends on soil to grow food, fiber, and other plants.A. Cropland – land on which soil is workedB. Grazing land – land used for grazing

cattle and sheep; perennial forage.C. Forests – land used for growing trees,

which is later harvestedD. Water structures – ponds and other

reservoirs are constructed out of soil.

Non-ag uses of soilA. Recreation – playgrounds, sports fields,

jogging paths, golf courses, parks, camp grounds,etc.

B. Foundations – buildings depend on a solid soil base upon which a building is to be built and remain sound.

C. Waste disposal – used for the treatment of human sanitary wastes.

D. Building materials – build underground, into hillsides, adobe

Five factors that affect soil formation A. Parent Material – type of rock that soil is

made from.

Igneous sedimentarymetamorphic

B. Climate – temperature & moistureC. Living organisms – organisms (bugs &

worms) and plants in the soil.D. Topography – hills and valleysE. Time or weathering – age of the soil and

climate

THE MAIN KINDS OF SOIL PARENT MATERIALS

Parent material is formed by the disintegration and decomposition of rock

A. Most soils in Illinois were formed by glaciers.

Newer and more productive

Older and less productive

B. About 64% of the soil is formed from loess. Loess occurred from theblowing of the soil after the glaciers.

C. About 7% of the state soil is due to recent stream deposits. This is referred to as alluvium.

D. Bedrock – most of the shale, sandstone, or limestone bedrock in Illinois is buried by loess. Except in extreme NW and Southern Illinois.

• Organic soils – less than 1% of the soils in Illinois are classified as organic. Occur where formerly shallow ponds or supported swamp vegetation. Wet conditions slow decay of organic materials. – Two types: muck and peat

Topography is the slope characteristics of land.

How do living organisms affect the soil?Organisms living in the soil, like plants,

insects and microbes actively affect soil formation.

• Native Vegetation has the greatest affect on the development of soil – plants that once grew in it.

• Two primary types– Tall grass prairie– Deciduous hard wood

forest

A. Prairie soils have a dark and deep surface layer. The roots of the prairie grass filled the top of the soil.

B. Timber soils tend to have a thin, moderately dark layer. Due to organic matter accumulating on the surface and decaying quickly.

Weathering1. Physical weathering

1. The affects of climatic factors such as temperature, water, and wind. Freezing and thawing are a major contributor.

Weathing (cont.)2. Chemical weathering

a. changes the chemical makeup of rock and breaks it down. Rainwater can dissolve minerals.b. Some minerals react with oxygen. Oxidation further decomposes rock.

Weathering (cont.)B. Weathering causes soil to:

1. Develop2. Mature3. Age

ClimateRefers to rainfall, freezing, thawing, wind,

and sunlight.

Climate (cont)B. The climate in Illinois is said to be of the

continental type. Hot Summers, Cold Winter

Climate (cont.)C. Rainfall and Wind wear the rock away a

little at a time.

Physical Features of soilSoils have many features that are used to

recognize the difference between them. They include:A. Texture – coarseness of fineness of soil

particlesB. Structure – the way in which soil particles are held togetherC. Depth of horizons – depth of each soilD. Color – darkness or lightness of soil color

ColorsA. Very Dark - ~5% O.M.B. Dark - ~ 3.5% O.M.C. Moderately Dark - ~ 2.5% O.M.D. Light - ~2% O.M.E. Very Light - ~1.5% O.M.

Soil TextureA. Soil Texture is the fineness or coarseness

of a soil.1. Sand – largest particle2. Silt – medium sized particle3. Clay – small particle

SandSilt

Clay

Texture (cont.)B. Texture is important because it affects:

1. Water holding capacity – the ability of a soil to retain water for use.

2. Permeability – ease with which air & water my pass through the soil.3. Soil Workability – the ease with which soil may be tilled and amount of time after rain.4. Ability for plants to grow, ie carrots

Texture (cont.)A. Soil texture may be determined in 2 ways

1. Using a textural triangle. This is found be using the percentage of each type of soil particle.

Textural Triangle

Ribbon Methoda. Fine texturedb. Moderately fine texturedc. Medium texturedd. Moderately coarsee. Coarse

Ribbon testing

Ball of clay made in fist Starting to form a ribbon Clay Ribbon (>2")

Starting to make a ribbon from sand Ribbons are hard to form with sand (<1")

Soil StructuresA. GranularB. CrumbC. PlatyD. Prismatic or ColumnarE. BlockyF. Structureless

1. Single grain2. Massive

Soil Structure

Soil Structure

Soil Structure

Soil Structure

Soil Structure

Soil Structure

Soil Structure

Soil ProfileI. A soil profile is a vertical cross section of

soil.A. Each layer may be differentB. A soil profile is usually studied to a depth of

3 to 5 feet.

Soil Profile

Changes in soilII. Soils change over time in response to their

environment.A. The causes can be classified as:

1. Additions2. Losses3. Translocation4. Transformation

Soil DegradationI. Soil Degradation is lowering the quality of

soil or loss of productivity. Occurs because people don’t understand the soil and consequences of its uses.Results from:

A. ConstructionB. ContaminationC. Erosion

ConstructionA. Construction is altering land by building:

1. Roads2. Houses3. Offices4. Factories5. Other Structures

ContaminationA. Results when chemicals, oil, and other

substances leak into the land.

D. Soil may be contaminated by Ag practices:1. Too much fertilizer2. Excess chemicals3. Irrigation water contains salt

Soil ErosionIV. Soil erosion is the process by which soil is moved.

A. Natural causes (natural erosion)1. Round off mountains, fills in valleysEx. Mississippi DeltaB. Human actions1. Human activity, such as construction & plowing may cause accelerated erosiona. removes topsoil at an excessive rate

Natural Erosion

Human actions accelerating

Soil Erosion

V. Other SourcesA. Improper irrigation practices

1. Salinization – accumulation of salts2. Alkalinzation – accumulation of sodium3. Waterlogging – supersaturation

B. Not replacing plant nutrientsC. PollutionD. Overgrazing, deforestation, desertificationE. Compaction

SummarySoil can be very fragileCare must be taken to produce cropsTakes many, many years, to make new soil

through weathering (1” > 1000 years)