Chapter 5 5.2 Soils

Characteristics of Soil Soil is part of regolith (loose materials that cover Earth) that supports the growth of plants There are three important characteristics to soil Composition Texture Structure

Characteristics of Soil- Composition Soil has four major components: Organic matter, or humus, which is the decayed remains of organisms Mineral matter, or broken-down rock Water (in pore spaces) Air(in pore spaces)

Characteristics of Soil- Composition In pore spaces between soil particles is air and water

Characteristics of Soil Organic Matter Organic matter is an important source of: plant nutrients and increases soil’s ability to hold water

Characteristics of Soil Mineral Part Soil Texture – refers to the proportions of the 3 different particle sizes: 1. Sand (large size) 2. Silt (medium size) 3. Clay (small size)

Soil Texture What type of soil consists of 10% clay, 60% silt, and 30% sand? Silty Loam Loam soil is the best for growing plants. Why? A loam soil contains equal parts sand, silt, and clay

Soil Formation Time Climate The longer the soil has been forming, the thicker it becomes Climate Greatest effect on soil formation Variations in temp and precipitation influence the rate, depth, & type of weathering

Soil Formation Organisms Plants are the main source of organic matter in soil Microorganisms, including fungi, bacteria, and single-celled protozoans, play an active role in decomposing dead plants and animals Burrowing animals mix the mineral and organic matter in soil

Soil Formation Slope On steep slopes, erosion is accelerated Little water can soak in, so the soil generally holds too little moisture for plant growth As a result, soils are usually ______ or __________. thin nonexistent

Soil Formation Flat areas often have very thick soil

The Soil Profile Soil horizons are zones or layers of soil A soil profile is a vertical section through all the soil horizons

Soil Profile

Soil Profile 1. A horizon Commonly known as “topsoil” 2. B horizon Its upper part is made mostly of loose leaves and dead plants 2. B horizon Commonly known as “subsoil” Contains fine clay particles

Soil Profile C Horizon Contains partially weathered parent material

What is Soil Erosion? Movement of topsoil down slope by the force of running water Erosion can also be caused by blowing of soil particles by wind, like on a beach

Soil Erosion Humans accelerate erosion by removing natural vegetation from land: Examples – 1. farming 2. logging 3. construction logging construction

Decreasing Soil Erosion Hillside Terracing

Decreasing Soil Erosion Plowing along the contours of a hillside

Decreasing Soil Erosion Planting rows of trees called windbreaks