Grade 7 Science Unit 4: The Earth’s Crust Soil

Soil Can take thousands of years to form. Many processes are involved in the formation of soil. Weathered and eroded rocks form the parent material of soils.

Organic material from the decomposition of plants and animals provide the nutrient base for a variety of soil ecosystems. Soil develops faster in warm climates.

3 Basic Types of Soil: Clay Sand Gravel The above are listed from the smallest to the largest particle size.

Factors that Determine how Soil Develops Refer to page 426

Porosity vs. Permeability The amount of empty space in a soil or rock. A measure of the ease with which liquids and gases pass through a soil or rock.

Soil Classification... Soil is classified according to their characteristics. These are usually based on texture or how they feel.

Coarse Texture: These soils have a sandy/ gravelly texture. They feel gritty and can roll between your fingers. Grains can be seen with the naked eye.

Coarse Soil Sand/ Gravel

Medium Texture: Also called loam. Farmers preference. Composed of sand, silt and clay in nearly equal proportions. May feel gritty and sticky at the same time.

Medium Grain Soil Loam

Fine Textured: Made up of clay. Feel greasy or sticky. Have little texture when wet.

Fine Grain Soil Clay

Fine Medium Coarse

Complete Core Lab Activity 12-2B Be a Soil Sleuth

Fertilizers Substances that provide nutrients for plants. May contain decomposed plants and animals and other minerals. Can have natural or human-made fertilizers.

Enriching Soils Compost Manure Chemical fertilizers Refer to page 435

Composting The breakdown of plant materials. (decomposition) Organic materials are piled together and under the right conditions will form humus.

Good Things to Compost

Enriching Soils... Positive effects Enhanced plant growth. This will decrease erosion, more food and better looking plants and crops.

Negative effects: Pollution in the form of run-off. Phosphate pollution in lakes and ponds may increase algal blooms. This removes oxygen and kills aquatic creatures.

Nitrogen compounds can also pollute water in the form of run-off.

Solutions: Refer in pages 437(8) Reduced reliance on chemical fertilizers. Limiting run-off Planting wind breaks No-till farming

Desertification The process in which nutrient depleted soils are formed through erosion of fertile soil. Solutions?