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SOIL Don’t Call it Dirt
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Soil Produced slowly ( years typically) by weathering of rock, deposition of sediments, and decomposition of organic matter. The formation of just 1 cm of soil can take years to renew depending on climate. Who cares about dirt????? All the food we consume depends upon the soil Soil is a habitat for many organisms (sometimes more biomass below than above the surface) Soil stores both water and nutrients for ecosystems Soil filters the water that passes through it and alters its chemistry Soil (the pedosphere) is “a thin bridge between the biosphere and the lithosphere”
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What is soil made from? Four main components
Mineral Particles from the underlying rock Organic remains that have come from plants and animals Water within the spaces between the grains Air within the spaces between the grains Soil is typically a 50:50 mixture of solids and pore space
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Soil Horizons – separate zones (horizontal layers) within soil
Oak tree Lords and ladies Soil Horizons – separate zones (horizontal layers) within soil Soil profile – cross-section view of soil Word sorrel Earthworm Millipede Fern Honey fungus O horizon Leaf litter A horizon Topsoil E horizon transition B horizon Subsoil C horizon Loosened material R horizon Hard bedrock Root system Red earth mite Mature soil Fig , p. 220
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Soil Horizons “Floors in the geological building of life underneath your feet.”
O horizon – surface litter Freshly fallen leaves, twigs, etc. (newly added organics) Fungi, bacteria, animals, etc. will start decomposition process A horizon – top soil Mixture of humus and inorganic materials such as clay, silt, or sand. Humus: Partially decomposed bodies of dead plants and animals. Normally dark brown or black The roots of most plants are concentrated in top 2 layers Releases water and nutrients slowly Provides aeration to roots Healthy soil contains many nematodes and bacteria, fungi, etc. (billions per handful)
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B – horizon and C - horizon
B – The layer where most of the decomposed matter and soluble minerals eventually deposit C- Weathered rock from which the soil forms R - Parent Material (Bedrock) R
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Immature soil Young soil Mature soil
Oak tree Lords and ladies Word sorrel Dog violet Earthworm Organic debris Builds up Grasses and small shrubs Millipede Rock fragments Mole Moss and lichen Fern Honey fungus O horizon Leaf litter A horizon Topsoil B horizon Subsoil Bedrock Immature soil Regolith C horizon Loosened Material Young soil Pseudoscorpion Mite Nematode Actinomycetes Root system Red earth mite Fungus Springtail Mature soil Bacteria Fig , p. 220
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Soil as a System
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