22 Lec 22 Soil Carbon2 - Part 2: Mineralization and residue...

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I. Factors controlling the rates of decomposition and mineralization 1. Location and size of residues 2. C/N of residues 3. Importance of soil fauna 4. Lignin content of residues 5. Environmental conditions in the soil II. Decomposition of organic residues 1. Decomposition in aerobic soils 2. Decomposition in anaerobic soils 3. Microbial succession 4. Kinetics of organic residue decay Soil Organic Matter Soil Organic Matter Part 2: Mineralization and residue decomposition Part 2: Mineralization and residue decomposition Reading : Textbook: Sylvia et al., 2004. Chapter 13, pages 306-318.
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Factors Controlling Rates of Decomposition and Mineralization 1. Location and size of residues Location in or on the soil Surface versus incorporated in soil? Particle size Big particle versus small particle?
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Factors Controlling Rates of Decomposition and Mineralization 2. C/N of organic residues C content of plant 42% N content of plant = <1 to >6% C/N plant residues: 10-30 to 600 Relative proportion (%) Cellulose Hemicellulose Lignin Proteins Fats, oils Sugars, amino acids Grass, legumes trees Younger plants Older plants High C/N Low C/N
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Factors Controlling Rates of Decomposition and Mineralization From Brady & Weil, The Nature and Properties of Soils. 2002. Days after killing cover crop 100 80 60 40 20 Percent cover crop tissue remaining 100 80 60 40 20 120 0 0 Cereal rye killed April 22 C/N = 38/1 Cereal rye killed April 8 C/N = 28/1 100 80 60 40 20 100 80 60 40 20 120 0 0 Days after killing cover crop Hairy vetch killed April 22 C/N = 10/1 Legume / cereal Young / older plant 2. C/N of organic residues
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Factors Controlling Rates of Decomposition and Mineralization 2. C/N of organic residues C/N of microorganisms: 8 Only 1/3 of C metabolized by microorganisms is incorporated into new biomass
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22 Lec 22 Soil Carbon2 - Part 2: Mineralization and residue...

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