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Soil Organic Matter.docx

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GEOG 317
Margaret Schmidt

SOIL ORGANIC MATTER Organic matter- humus- complex and resistant to decay - brown and dark brown - amorphous- or has no form - colloidal - results from microbial decomp and synthesis - water retention is higher than for mineral soils - has chemical and physical properties of great significant to soils and plants Sources- plant residues, animals, compost and manures, sewage sludge - has dry matter- 25%, rest is water- 60-90% - dry matter has mostly cellulose, with other protein and lignin etc elements such as mostly carbon and oxygen with hydrogen - Rates of decomp based on how complex the molecular structure is : - sugars, starch and proteins quick decomp, fats and waxes- slow decomp - PROCESS OF DECOMP: - 1. Bulk of organic material undergoes an enzymatic oxidation- called respiration 2. Essential elements such as nitrogen, phosphorous and sulfur are mineralized or immobilized 3. Compounds relatively resistant to microbial action are formed- soil humus - Mineralization- conversion of an element from organic to inorganic form as a result of microbial decomp - Immobilization- conversion of an element from inorganic to organic form in microbial tissues, making element unavailable to plants Factors controlling rates of decomp and mineralization: - environmental conditions in soil such as pH, soil moisture, aera
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