NRES 201 Lecture 12 Outline of Last Lecture I Interpretive classification of soils II Geographic information systems Outline of Current Lecture III Review of Previous Coverage IV Revisiting Texture V Soil Density Current Lecture Review of Previous Coverage Soil s basic physical properties Color o Described by hue value and chroma Texture o Size distribution of soil particles Structure o Arrangement of soil particles to form aggregates or peds Consistence o Cohesiveness holding soil particles together Soil components The soil solids o Inorganic minerals Primary minerals present in the original rock Secondary minerals formed by weathering o Organic matter Living organisms biomass Organismal remains residues Decay products humus The soil solution o Consists of water dissolved ions molecules and gases o Medium for chemical and biological processes o Vital to plant growth These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Held within soil pores Mobile in large pores Immobile in small pores The soil atmosphere o Consists of gases that occupy soil pores not filled with water o Isolated not continuous o Differs from ambient air by having Less O2 More CO2 More Humidity o Critical to biological processes Texture Particle Size Analysis o Sieve soil to 2 mm o Removes course particles o Based on Stokes law v kd 2 where v the settling velocity k a constant that depends on water temperature and particular density d the particle density Surface area and soil processes o Greater surface area enhances Water retention In soil pores or as surface films Adsorption Surface adhesion of gases or dissolved ions or molecules Weathering Exposure allows chemical or microbial attack Aggregation Surface cohesion of soil particles Microbial activity Microbes colonize surfaces Soil Density Density The weight or mass of an object divided by its volume which is expressed as g cm 3 Particle density o The mass per unit volume of dry soil solids o Does not include the volume between particles o Unaffected by pore space soil structure tillage compaction Bulk density o The mass per unit volume of dry soil
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