Chapter 1 Environmental Soil chemistry What is soil 435 1.pdfChapter 1 Environmental Soil chemistry INTRODUCTION What is soil? Soil is a natural mixture of inorganic and organic solids, air, water, and microorganisms.

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  • Chapter 1 Environmental Soil chemistry

    INTRODUCTION What is soil? Soil is a natural mixture of inorganic and organic solids, air, water, and microorganisms.

    All these phases, influence each other, they also interact with the rest of the environment.

    Reactions in the soils solids affect water and air quality, water and air weather the solids,

    and microorganisms catalyze many of the reactions. Soil chemistry involves all these

    reactions but emphasizes on the soil solution that is, the thin aqueous film surrounding

    soil particles.

    Soil-ion interactions The study of soil chemistry was first started by people who were interested in plant

    growth and crop production, that is soil fertility specilists. However, soil chemistry

    became a separate (though related) field from soil fertility about one hundred and fifty

    years ago when cation exchange reactions in soils were discovered. From that point

    people realized that soils could be studied apart from plants, yet the results would still

    have implications for plant growth, soil fertility, and environmental quality.

    A T M O S P H E R E

    Dust PLANTS

    Dead biomass H2O solutes

    H2O solutes

    H2O CO2 N2

    O2, pollutant gases

    SOIL Air (O2, CO2) SOIL

    Solution

    H2O Solutes

    unsaturated zone

    ground water

    SOIL Inorganic and Organic colloids

    TPSS

    435

  • As you know, the immediate sources of nutrients that plants can take up are solutes,

    electrolytes, and non electrolytes in the soil solution. There are many processes that can

    control the entry of ions and molecules into the soil solution. Some of the major

    processes are:

    1. Mineral weathering, for example the dissolution of feldspar to form kaolinite.

    2KAlSi3O8 + 9H2O + 2H+ = Al2Si2O5(OH)4 + 2K+ + 4Si(OH)4 2. Organic matter decomposition that releases N, S and many other nutrients;

    complication of metals by organic acids.

    3. Irrigation and rain that add salts to the soil.

    4. Fertilization, liming.

    5. Adsorption, desorption by clays, for example, phosphate sorption, potassium

    fixation.

    6. Oxidation/reduction (redox)

    Fe3+ + e- Fe2+

    amino acid CH3-CH-COOH + 1/2O2 CH3CO- COOH + NH3 NH2 ( alanine ) oxidize (pyruvic acid )

    Cu2+ +

    -OOC R -OOC

    O Cu C=O O R C O

    TPSS

    435

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