sw28 - Soil Organic Matter and Organic Colloids Organic...

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Soil Organic Matter and Soil Organic Matter and Organic Colloids Organic Colloids
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Soil Organic Matter Living Biomass Plant/Animal Residues Complex Organics (unidentifiable) Humic and Non-humic
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Accumulation of partially disintegrated and decomposed plant and animal residues as well as living biomass . Decomposition principally by soil microorganisms Transitory soil constituent (hours to 100s of years) Requires continual addition to maintain O.M. levels. 1 – 5% (by weight) in a typical, well-drained mineral soil Soil Organic Matter Soil Organic Matter
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Increases water-holding capacity/porosity Can increase infiltration rates. Aids in soil aggregation, structure Principal source of essential plant nutrients Energy source for soil microorganisms Soil Organic Matter Soil Organic Matter
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Soils and Global Carbon
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Carbon Carbon Soils contain more than 4x more Carbon than all vegetation combined.
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Amounts Amounts 2400 petagrams (10 15 g) in soil 700 petagrams as soil carbonates Storage of earth carbon Gelisols
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Composition
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Plant-Derived Organic Matter Carbon (42%) Hydrogen (8%) Oxygen (42%) Nitrogen, Sulfur, Phosphorus, Potassium
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Composition Composition plants elements compounds
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Sugars, starches Crude proteins Hemicellulose Cellulose Fats, waxes Lignins, phenols Compounds Rapid Decomposition Slow Decomposition Decomposition
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Majority of breakdown results in Carbon dioxide, water, energy and heat Essential elements (N, P, S) are released This is called “mineralization” Highly resistant compounds are formed which remain in the soil for long periods: “humification” Decomposition The biochemical breakdown of mineral and organic materials. Some of the substrate carbon is incorporated into the cells of microorganisms: called “immobilization”
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Carboniferous Period About 350 million years ago “the age of swamps and coal" First land plants: 480 mya.
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