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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<ul><li><p>Chapter 1 Environmental Soil chemistry </p><p> INTRODUCTION What is soil? Soil is a natural mixture of inorganic and organic solids, air, water, and microorganisms. </p><p>All these phases, influence each other, they also interact with the rest of the environment. </p><p> Reactions in the soils solids affect water and air quality, water and air weather the solids, </p><p>and microorganisms catalyze many of the reactions. Soil chemistry involves all these </p><p>reactions but emphasizes on the soil solution that is, the thin aqueous film surrounding </p><p>soil particles. </p><p> Soil-ion interactions The study of soil chemistry was first started by people who were interested in plant </p><p>growth and crop production, that is soil fertility specilists. However, soil chemistry </p><p>became a separate (though related) field from soil fertility about one hundred and fifty </p><p>years ago when cation exchange reactions in soils were discovered. From that point </p><p>people realized that soils could be studied apart from plants, yet the results would still </p><p>have implications for plant growth, soil fertility, and environmental quality. </p><p> A T M O S P H E R E </p><p> Dust PLANTS </p><p>Dead biomass H2O solutes </p><p>H2O solutes </p><p>H2O CO2 N2 </p><p>O2, pollutant gases </p><p>SOIL Air (O2, CO2) SOIL </p><p>Solution </p><p>H2O Solutes </p><p> unsaturated zone </p><p> ground water </p><p>SOIL Inorganic and Organic colloids </p><p>TPSS</p><p> 435</p></li><li><p> As you know, the immediate sources of nutrients that plants can take up are solutes, </p><p>electrolytes, and non electrolytes in the soil solution. There are many processes that can </p><p>control the entry of ions and molecules into the soil solution. Some of the major </p><p>processes are: </p><p> 1. Mineral weathering, for example the dissolution of feldspar to form kaolinite. </p><p> 2KAlSi3O8 + 9H2O + 2H+ = Al2Si2O5(OH)4 + 2K+ + 4Si(OH)4 2. Organic matter decomposition that releases N, S and many other nutrients; </p><p>complication of metals by organic acids. </p><p>3. Irrigation and rain that add salts to the soil. </p><p>4. Fertilization, liming. </p><p>5. Adsorption, desorption by clays, for example, phosphate sorption, potassium </p><p>fixation. </p><p> 6. Oxidation/reduction (redox) </p><p> Fe3+ + e- Fe2+ </p><p> amino acid CH3-CH-COOH + 1/2O2 CH3CO- COOH + NH3 NH2 ( alanine ) oxidize (pyruvic acid ) </p><p> Cu2+ + </p><p>-OOC R -OOC </p><p> O Cu C=O O R C O </p><p>TPSS</p><p> 435</p></li></ul>