Lecture 12 Iron, Aluminum, Organic Matter

Lecture 12 Iron, Aluminum, Organic Matter - Organic Matter...

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Unformatted text preview: Organic Matter 1. Aluminosilcates are composed of two fundamental units: silica tetrahedra and aluminum octahedra to form sheet-like structures. 2. Cation substitutions can take place in either the tetrahedral sheet or the octahedral sheet which result in negative charge on the mineral. 4. Positively charged cations are attracted to the negative sites on clay minerals which can function as storage for important plant-essential nutrients. 5. Preference for cations at mineral surfaces is dictated by charge, concentration in solution and size of the cation. 3. The total number of negative sites on clay minerals is represented by the Cation Exchange Capacity (CEC). Flocculation means to bring particles together Dispersion pushes particles apart.- charge- charge- charge Al 3+ Al 3+ Al 3+ 2000 B.C. Na + Na + Na + Na + Na + Na + Na + Na + Na + Small, higher-charged cations tend to flocculate clay particles. Large cations with low charge tend to disperse clay particles Ca 2+ , Mg 2+ , Al 3+ Na + , K + Iron oxides originate from iron-bearing primary or secondary minerals. Reduced iron (Fe 2+ ) occurs in low-oxygen environments and results in a greyish color. Oxidized iron (Fe 3+ ) occurs in high oxygen environments and results in orange-red colors. Water restricts diffusion of oxygen in soils Grey colors interspersed with orange-red colors often indicates the presence of water tables in soils. Iron and Aluminum Oxides Can possess negative, positive, zero charge Potential interaction with cations and anions Cl-, F-, Br-, SO 4 2-, NO 3-, CO 3 2-, PO 4 3-Anion Exchange Silicate clays possess negative charge due to isomorphous substitution during the formation of the mineral. Iron and aluminum oxides are products of weathering and can possess negative positive or zero charge. Charge derives from Interaction with hydrogen ions in solution. Cation Exchange Cation or Anion Exchange Silicate Clays vs. Al/Fe oxides Soil Organic Matter and Soil Organic Matter and Organic Colloids Organic Colloids Organic matter plant debris or litter in various stages of decomposition and includes the living organisms in the soil Accumulation of partially disintegrated and decomposed...
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This note was uploaded on 07/31/2011 for the course SOS 3022 taught by Professor Staff during the Fall '08 term at University of Florida.

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Lecture 12 Iron, Aluminum, Organic Matter - Organic Matter...

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