Science Chapter 7 - section 3

Name the 5 factors of soil formation.

1. Climate 2. Topography 3. Parent material 4. Biological activity 5. Time These factors combine to produce different types of soil called soil orders. The factors of soil formation results in to 12 different soil orders.

Name the 4 major soil horizons.

1. O horizon - top layer of organic material which is humus and leaf litter. 2. A horizon - weathered rock combines with dark brown organic material. 3. B horizon - also called the zone of accumulation. It is a red or brown layer that has been enriched over time by clay and minerals deposited by water flowing from the layers above. This layer has a blocky structure and can have a hard layer called hardpan which allows no water to pass through. 4. C horizon - contains little or no organic matter and is often made of broken down bedrock. Each of these layers depends on the factors of soil formation.

What is a soil horizon?

A distinct layer within a soil profile. There are 4 major soil horizons.

What is a soil profile?

A vertical sequence of soil layers. Digging a deep hole in the ground will reveal this. New soil doesn't have distinct layers and are called undeveloped soils. Mature soils have distinct layers although this takes 1000's of years to develop.

How are particles of soil classified?

According to size as clay, silt or sand. Clay is the smallest and sand is the largest. Soil texture affects the soils capacity to accept rain and hold moisture and the soil texture also varies with depth.

Parent material is often what?

Bedrock. As the parent material weathers, the weathering products rest on top of the parent material. Over time, a layer of the smallest pieces of weather rock develops above the parent material. Eventually living organisms such as plants and animals become established. Rainwater seeps through this top layer and dissolves soluble minerals carrying them into the lower layers of soil.

What is the most significant factor controlling development of soil?

Climate. Temperature, wind and the amount of rainfall determines the type of soil.

Explain how biological activity effects soil formation.

Different types of living organisms in soil can result in different soil orders. Fungi, bacteria, plants and animals interact with the soil. Microorganisms decompose dead plants and animals. Plant roots can open channels and when they decompose, they add organic material to the soil. Sometimes different types of living organisms in the same soil can result in different soil orders.

What is decaying organic matter called?

Humus. This serves as the overlying bedrock of earths surface and is a medium for the growth of plants.

Soil color examples.

In the O horizon and the A horizon the soil is dark colored because of the rich material. Red and yellow soils might be from oxidation of iron minerals. Yellow soils are poorly drained and are associated with environmental problems. Grayish or bluish soils are common in poorly drained regions where soils are always wet and maybe leached (without) minerals and oxygen.

Use a soil triangle to identify soil texture.

LOOK AT PAGE 182 IN BOOK.

What develops during the process of soil formation?

Layers. Most of the volume of soil is formed from the weather products of a source rock called parent material.

What do scientists use to determine soil color?

Munsell system of color notation. It consists of 3 parts: hue which is the color value which is lightness or darkness chroma which is intensity.

How does time effect soil formation?

New soils, such as entisols, are found along rivers, where sediment is deposited by periodic flooding. These soils had little time to weather and develop soil horizons. Older soils, such as ultisols, develop over tens of thousands of years and most of their original minerals in the soil have changed or been washed away. These are red colored soils.

Explain soil development.

Often begins when weathering breaks solid bedrock into smaller pieces. These pieces of rock continue to weather and break down into smaller pieces. Worms and other organisms help break down organic matter and add nutrients to the soil. As nutrients are added to the soil, the texture changes and the soils capacity to hold water Increases.

Explain how topography effects soil formation.

On Steep slopes, weathered rock is carried downhill by erosion which means that hillsides have shallow soils and valleys and flat areas develop thicker soils with more organic material. In the northern hemisphere, slopes that face the south receive more sunlight which allows vegetation to grow. Slopes without vegetation tend to lose more soil to erosion.

What is transported soil?

Soil that develops from parent material that has been moved far from its original location. For example, sediments from Canada transported to the US by glaciers.

What is residual soil?

Soil whose parent material is local bedrock. For example, Kentucky's bluegrass soil.

What is soil?

The loose covering of weathered rock particles and decaying organic matter

What is soil fertility?

The measure of how well a soil can support the growth of plants.

What determines the soil color?

The minerals,organic matter and the moisture on each soil horizon.

What is soil taxonomy?

The system scientists use to classify soils into orders and other categories.

What factors affect soil fertility?

Topography Availability of minerals and nutrients The number of microorganisms present The amount of precipitation The level of acidity