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23 Lec 23 Soil Carbon3

23 Lec 23 Soil Carbon3 - Soil Organic Matter Soil 3...

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I. Humus formation and characteristics 1. Humus formation 2. Humus characteristics a. Composition b. Chemical fractionation c. Humus-clay complexes b. Adsorptive properties 3. Beneficial properties imparted to soil by humus II. Composting Reading : Textbook: Sylvia et al., 2004. Chapter 13 (pages …) and Chapter 23 (pages 587-598) Soil Organic Matter Soil Organic Matter 3: Humification and Composting 3: Humification and Composting
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Plant Residues Soil Biota Humus *Decomposition *Humification *process *Recycling Carbon Dioxide *Respiration (oxidation) Decomposition Sequence
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Humus http://virtual-museum.soils.wisc.edu/som/index.html Brown to black colored Very large molecules (MW: 2,000-300,000 g/mol) Relatively stable, complex, polymeric
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Humus Formation From Sylvia et al., Principles and applications of soil Microbiology. 2004. Least understood aspect of SOM chemistry Precursors are enzymatically produced/altered Synthesis: condensation into larger molecules
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Humus Composition Phenolic units (50%), polysaccharides (20%), and proteins (20%) 58% C, 3-6% N; C/N/P/S ratio: 100/10/1/1 < 50% of its structural composition are known Age of soil humus: 150- 1500 years = fulvic acids + humic acids + humins
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Humus Composition Light yellow Yellow brown Dark brown Grey- black Black Fulvic acid Humic acid Humin Humic substances decrease in degree of solubility soluble in water at all pHs insoluble at pH<2, soluble at high pHs insoluble in water at all pHs Chemical fractionation :
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