3.2 - Soils Discuss why soil is an important resource. Describe how soil forms from existing rocks. Describe the different textures and components of soil.

What is Soil? Soil is a complex mixture of organic and inorganic materials. Inorganic materials weathered rock (pebbles, sand, silt, clay particles) Organic materials remains of partially decomposed plants and animals Provides nutrients, such as nitrogen, needed for plant growth Soil is an ecosystem unto itself. Earthworms, bacteria, insects, fungi, etc. call soil home

Factors that Influence Soils Climate Rock Type Topography Biological Activity Time

1. Climate Most important factor determining soil type Different rock types in a given climate produce similar soil Warmer, wetter climates = greater rate of weathering higher rate of chemical and mechanical weathering Plants and bacteria grow faster Thicker soils with more organic materials Colder, drier climates = lower rates of weathering Thin soils with less organic materials

2. Rock Type (Parent Material) Parent Material = source of inorganic materials Chemical changes during soil formation depend on what minerals and rocks are present in the parent material. Example: Calcium-rich soils generally form from calcium-rich rocks (like limestone) but not from calcium-poor rocks like granite.

3. Topography Loose soil stays in place in flat areas, allowing more thorough physical and chemical alteration of its grains. On steep slopes, the soil moves downhill before complete alteration can occur.

4. Biological Activity Plant roots physically break rocks into small pieces. Lichens dissolves rock. Burrowing animals and insects mix the soil and help aeration. Humus = the decayed remains of plant and animal life increases the soil’s porosity and water holding capacity helps to buffer rapid changes in soil acidity helps the soil to hold its nutrients, increasing its fertility Lichens Earthworms in Humus

4. Biological Activity

5. Time When bedrock is exposed at the surface, chemical, biologic, and physical processes combine to produce a thin soil layer. Over time, the processes extend vertically downward, developing soil horizons whose position and thickness change over time.

Soil Texture and Composition Permeability ability of soil to allow water to flow easily through the spaces between soil particles influenced by soil texture Soil Texture depends on particle size and proportion of particle types in the soil particle types = sand, silt, clay, gravel

Identifying Soil Types by Texture When soil scientists want to precisely determine soil type, they measure the percentage of sand, silt, and clay. The soil type can then be determined from the location on the diagram.

Soil Profile The simplest profiles have only 3 soil horizons: A Horizon (topsoil) region of most intense biological activity contains highest amount of organic material A B Horizon (subsoil) where soluble minerals and clays accumulate. holds more water than the topsoil because of the presence of iron and clay minerals. less organic material B C Horizon layer of partially altered bedrock Pieces of the original rock are seen and can be identified. C

Types of Soils Influenced heavily by climate Include pedalfer, laterite, and pedocal

Soil Conservation

Soil Conservation Harmful Human Practices Deforestation Over-Farming Pollution

Soil Conservation Positive Human Practices Add organic materials to soils (compost, manure) Crop rotation and Cover crops Terracing Planting trees as windbreaks Plowing along contours of the field

Soil & Interaction of Earth’s Systems Dew (moisture from the air) begins chemical alteration of parent rock Rain erodes loose soil, preventing further alteration Temperature controls rate and extent of chemical processes Soils Biosphere Hydrosphere Geosphere Atmosphere plants add and remove chemicals plant roots anchor soil in place, enabling chemical reactions to be completed animals mix soil; transport seeds, etc. Water seeps into the ground, dissolving and redistributing elements evaporation dries soil, changing its physical characteristics solid rock and unconsolidated sediment are the parent material for soil geologic processes (surface and internal) expose and bury rock, etc.