WHAT’S IN THE SOIL?

And why is it important?

Sand

Drains well but can not hold onto nutrients. Sand is a large particle.

Form lightweight, free-draining soils. Sand is an important part of the soil

because it provides drainage.

Silt

Can hold water but can be hard to drain. Can hold limited nutrients. Silt is a medium particle.

Silt is an important part of the soil because it holds limited nutrients and retains (holds onto) water.

Clay

Holds water well but can become heavy and waterlogged when wet. Can hold nutrients. Clay is a small particle.

Clay is an important part of the soil because it can hold nutrients and water.

All soils contain sand, silt, and clay but in differing amounts.

Air

Fills all gaps in the soil and allows plant roots and animals to breathe. 35-40% of a good soil is air. Air is a gas.

Important because it allows plant roots and animals to breathe.

Water

Clings to soil particles and gets soaked up by plant roots.

Without water, plants and animals would die.

Organic Matter

decaying animals and plants, and waste from animals. Releases nutrients slowly as it rots and

improves water holding. Improves water holding and helps the

soil stick together.

Animals

Includes insects, bacteria, and earthworms.

Help rot down decaying material.

5 FORMING FACTORS OF SOIL

Time

Landscape

Living Organisms (Biota)

Climate

Parent Material

Parent Material

Parent material refers to organic (such as fresh peat) and mineral material in which soil formation begins

Climate

a major factor in determining the kind of plant and animal life on and in the soil.

It determines the amount of water available for weathering minerals.

influence on soil temperature, determines the rate of chemical weathering. Warm, moist climates encourage rapid plant growth

and thus high organic matter production. The opposite is true for cold, dry climates. Organic matter decomposition is also accelerated in

warm, moist climates. Under the control of climate freezing, thawing, wetting,

and drying break parent material apart.

Living Organisms

Plants affect soil development by supplying upper layers with organic matter

recycling nutrients from lower to upper layers, and helping to prevent erosion. 

deep rooted plants contribute more to soil development than shallow rooted plants because the passages they create allow greater water movement

Landscape

Landscape position causes localized changes in moisture and temperature

Steepness, shape, and length of slope are important because they influence the rate at which water flows into or off the soil.

Time

The longer a soil surface has been exposed to soil forming agents like rain and growing plants, the greater the development of the soil profile.

Soil

If you look on a roadside cut, you will see various layers in the soil. These layers are called soil horizons. The way these layers are arranged is known as a soil profile. Soil scientists, who are also called pedologists, observe and describe soil profiles and soil horizons to classify and interpret the soil for various uses.

Soil Horizons

Soil scientists use the capital letters O, A, B, C, and E to identify horizons (layers). Most soils have three major horizons -- the surface horizon (A), the subsoil (B), and the substratum (C). The letter E is used for subsurface horizons that have a significant loss of minerals.

Soil horizons show different properties of soil such as color, texture, structure, and thickness.