Soil 5.2

What is soil? Soil is the mixture of bits of rock and once-living parts of plants and animals. Soil covers most of Earth’s landmasses. Without soil, plants and animals would not be able to live on land.

What does the term organic mean? Organic means having to do with or coming from living things.

Soil Horizons Each layer of soil is called a soil horizon.

Let’s look at the Soil Horizons diagram on p. 243. Horizon A- Holds most of the nutrients. It contain humus. Humus is the part of the soil that is made of decayed organic materials. This soil is called topsoil. Horizon B- This is the subsoil. It contains fine particles of rock. Horizon C- Made up of mostly large pieces of weathered rock.

Use the Soil Horizon diagram to answer the following questions. Which layer of soil do you think contains the most living organisms? A horizon Why do you think more organisms are in this layer? It contains the most oxygen. What are two reasons for the A horizon’s being deeper in a location where the ground is covered with plants? More plants die and add to the humus. Growing plants prevent the erosion of topsoil.

How is soil used? Different areas have different types of soil. The U.S. is mostly made up of 3 types of soil: Forest soil Desert soil Grassland and prairie soil

Forest soil Forest soil has a thin layer of topsoil with little humus. Frequent rainfalls bring the nutrients deep into the soil. Plants with shallow roots cannot reach the minerals and do not grow well. Most of the forest soil in the U.S. is in the eastern part.

Desert soil This soil is sandy and does not contain much humus. Deserts are dry and receive little rainfall. Plants that grow in a desert have special adaptations to help them survive. The desert soil is rich in minerals.

Grasslands and Prairies soil This soil is found between the Rocky Mountains and the eastern forests in the U.S. It is rich in humus and crops such as corn, wheat, and rye grow well in this soil.

Soil is a resource. It can be used up, wasted, or spoiled. Soil erosion can occur by wind and flowing water. Plants keep soil from eroding away. Plants remove the nutrients in soil and use this nutrients to grow. As plants die, the nutrients are returned to the soil.

Pollution Pollution is the addition of harmful materials to soil, air, or water. Soil can be polluted by chemicals placed in the ground. Chemicals used to kill insects and weeds can pollute the soil. Garbage can also pollute soil.

How is soil conserved? Conservation is the preservation or protection of natural resources. Methods for conserving soil: Fertilization, crop rotation, strip farming, contour planting, terracing, wind breaks, laws, individual efforts, and education

Fertilization Fertilizers can be added to soil to increase or replace nutrients.

Crop rotation Farmers can rotate the types of crops they plant each year. They can choose plants that add the nutrients that have been removed back into the soil.

Strip farming Farmers can plant grasses between rows of crops to help prevent soil erosion.

Contour Plowing Farmers can plow across a slope instead of down a slope. Rainwater carries rich topsoil down a hill and by contour plowing the flow of water can be slowed down.

Terracing Terraces are flat shelves that are cut into a hillside.

Wind Breaks To keep wind from blowing away topsoil, farmers plant tall trees along the edges of farmland.

Laws Governments pass laws to stop the pollution of soil.

Individual efforts We can all help stop the pollution of soil by helping keep the land clean and disposing of trash properly.

Education We can help inform others of the value of soil and how to conserve it.

Let’s Review with a few questions. What are the main steps in soil formation? Weathering of rock, breakdown of rock by microorganisms, growth of plants, and decay of plants and animals

How could erosion change soil horizons and how plants grow in that soil? Erosion can remove the rich topsoil that plants depend on for nutrients.

What properties of soil are best for farming? High humus and mineral content, and the ability to hold water

How might insect pests be controlled without using chemicals that may pollute the soil? The natural predators of the insects might be introduced to the location. Insect-resistant crops might be developed and planted.

What methods are used to conserve soil? Fertilizing, crop rotation, strip farming, contour plowing and terracing, wind breaks, laws, personal efforts, and education

What might cause mountaintops to have little or no topsoil? Topsoil is on the surface of the land. On a mountaintop, rain can easily wash soil down the slope.