Chapter 5 5.2 Soils

Characteristics of Soil Soil is part of the 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: Mineral matter, or broken-down rock Organic matter, or humus, which is the decayed remains of organisms Water Air

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 Water also provides nutrients Desert soils only contain a tiny amount of organic matter

Characteristics of Soil Mineral Part Soil Texture – refers to the proportions of different particle sizes Sand (large size) Silt Clay (small size) Loam (a mixture of all three sizes) is best suited for plant life Why is loam the best for plant growth? Loam provides the best of all worlds… it doesn’t dry out fast but doesn’t retain too much water.

Soil Texture What type of soil consists of 10% clay, 60% silt, and 30% sand? Silty Loam

What type of Soil do we have? Silt-60% Clay-20% Sand-20% Silt-10% Clay-60% Sand-30% Silt-33% Clay-33% Sand-34% Silt-20% Clay-30% Sand-50% ¼ clay, 4/8 sand, 2/8 Silt Make up three of your own and trade with a friend. Try to make it tricky!

Now it’s your turn! Make up three of your own and trade with a friend. Try to make it tricky!

Soil Formation Parent Material – source of mineral matter Time Climate The longer the soil has been forming, the thicker it becomes Climate Greatest effect on soil formation

Soil Formation Organisms Plants-main source of organic matter in soil Microorganisms decompose 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 A horizon Soil horizons - zones or layers of soil Soil profile - vertical section A horizon topsoil Upper part - mostly loose leaves and dead plants

Soil Profile B horizon C horizon fine clay Between B and the unaltered parent material partially weathered parent material

What is Soil Erosion? Movement of topsoil down slope by the force of running water or wind

Soil Erosion Rates of Erosion Humans accelerate erosion by removing natural vegetation from land: Examples – farming, logging, and 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