I SOIL COMPONENTS
Soil – top few inches of the earth’s crust.
Four Major Soil Ingredients:
1) Mineral matter – 45%- clay, sand, silt particles
2) Organic matter – 5% - living and dead plants and animals.
3) Air – 25%
4) Water – 25%
1) Mineral Materials
Mineral soil – high in mineral content, usually 6 to 12% organic matter.
Organic soil – high in organic matter, greater than 20% organic matter.
Minerals – inorganic elements or compounds that naturally occur.
- Sometimes form crystals (quartz and feldspar)
- Come from rocks and materials that have weathered.
- Form particles known as sand, silt, and clay.
Sand
- Soils higher than 85% sand are known as sand
- Largest sized mineral particle
- .05 to 2 mm (millimeters) in diameter
- Made of quartz
- Silicon dioxide (SiO2)
- Does not hold water well
- Water drains easily
- Not fertile (washes nutrients away)
Silt
- Smaller than sand but larger than clay
- .002 to .05 mm in diameter
- Fill spaces between sand particles
- Sometimes deposited by water when land is flooded
- Washed into oceans where streams empty
- Mississippi river delta (silt settling from Mississppi River)
Clay
- Smallest particle in soil
- Less than .002 mm in diameter
- Various minerals found in clay
- Fills spaces between silt and sand particles
- Gives soil ability to hold water
- More total surface area and space between particles compared to sand
Other minerals
- These minerals become plant nutrients
- Often added in fertilizer
- Calcium, phosphorus, potassium, nitrogen
2) ORGANIC MATTER
- Well decomposed organic matter is humus
- Decaying organic matter releases nutrients
- Plowing in crop residue incorporates organic matter
- Makes soil more productive
- Better soil tilth (tillage, workability)
- Increases chemical capacity of soil (ionic exchange)
- Increases nutrients available for plant growth
- Animal manure provides organic matter
- Tree leaves provide organic matter but may decay too rapidly
3) WATER
- Important nutrient for plant growth
- Adhere to surface of soil particles (adhesion)
- Soils too wet or too dry will not support plant growth of most crops or ornamental plants
- Amount of moisture needed varies with kind of plant
- Hydroponics – plants grown with roots in a nutrient solution
4) AIR
- Fills spaces between soil particles
- Plant roots need balance of air and water to survive
II NATURE OF SOIL
1) Physical Nature of Soil
- Physical qualities give workability required to culture crops
A) SOIL TEXTURE
- Proportion of sand, silt, and clay in the soil
- All soils are mixtures of sand, silt, and clay
- Ribbon Test (feeling of soil sample to determine texture)
- Soils are named on the basis of content
- LOAM (soils that are nearly equal parts of sand, silt, and clay) (40% sand, 40% silt, 20% clay)
- Soil triangle is used to explain make up of soil
- Sandy loam, silty clay loam, silt loam, sandy clay loam, clay loam, sand, loam, clay)
B) SOIL STRUCTURE
- Arrangement of soil particles into shapes
- Platy (layers), columnar, prismatic, blocky, and granular
C) SOIL TILTH
- Physical condition of the soil
- Related to soil content and made artificially by plowing
- Disks, harrows, etc. used for seedbed preparation
D) SOIL CONSISTENCY
- Vary according to feel and amount of effort needed to break a small clod
2) CHEMICAL NATURE OF SOIL
- Soil contains various chemical elements
- Some are essential for plant growth
- Too much of any element poses a problem
- pH refers to acidity or alkalinity (basicity)
3) BIOLOGICAL NATURE OF SOIL
- Most soils contain living organisms such as bacteria, fungi, plants, and animals
FUNCTIONS OF SOIL ORGANISMS
- Break down organic matter
- Aeration of soil
- Add fertility
III SOIL FORMATION
- Soil develops gradually over many years
- May take 1,000 years to develop one inch of topsoil
1) Parent Material
- Material from which soil develops
- Materials include rocks, specific minerals, and peat
- Peat (decaying plant material found in wet places – bogs)
- Shale and slate form soils high in clay
- Limestone forms shallow soil that may not be good crop land
- Sandstone forms sandy soils
- Parent material may be moved before soil is formed
- May be washed from one place to another
- May be blown from one place to another (LOESS)
- Glaciers, gravity, and lake deposits are sources
2) Weathering
- Process of changing materials into soil
3)Climate
- Long term weather conditions in an area influence soil development
4)Plants and Animals
- Organisms that grow on and in the soil influence development
- Leaves, stems, roots decay to form organic matter
- Dead animals decay to form organic matter
5) Slope and Drainage
- Lay of the land influences formation of soil