FANR 3060 1st Edition Lecture 10Outline of Last Lecture I. Soil Orderscon’tOutline of Current LectureI. Soil Physical PropertiesII. Soil TextureIII. Soil StructureIV. Soil DensityChapter 4I. Soil Physical Propertiesa. Soil is an arrangement of solids and poresi. Solids: various-sized particles of primary and secondary mineralsii. porous materialiii. Pores are important in root growth and water flow/holdingiv. Rocks have no poresII. Soil Texturea. Texture: mixture of particle sizes that make up a soil materiali. Percentage of sand, silt, and clay particles in a soilb. MOST IMPORTANT soil propertyi. Key property affecting all other propertiesThese 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.c. Particle size distributiond. Sand and silti. Mostly primary mineralsii. “inherited” from parent materialiii. Low surface area, low reactivity1. Inerte. Clay/Colloidsi. Colloids: very fine particles that don’t settle in waterii. Less than 2 micrometers in sizediii. Secondary mineralsiv. Formed during weatheringv. High surface area, high reactivity1. Charged particlesvi. Colloidal properties1. Don’t settle in water2. Plastica. Can be formed into ribbons3. Hold water and ions on surfaceIII. Soil Structurea. Structure: arrangement of primary soil particles (sand, silt, clay) into aggregates (aka peds)b. Granulari. Common in A and Aphoriz1. Usually in soils high in humus – mollic and umbricii. Peds are rounded, friable, and porousiii. Humus-clay interactions1. Polyvalent cation bridgingiv. Big in soil managementv. Plant roots and and fungi important in granular formationc. Blockyi. Common in B horizii. Created by flow of percolating water through horiz1. Creates flow paths that consolidate into blocky unitsiii. Important in water flow in subsoils1. Good water infiltration lessens erosioniv. Made of illuvial clay mineralsv. Fe coatings on ped surfacevi. All B horiz in GA are acid argillicIV. Soil Densitya. Influenced by tecture and structure as well as managemt history of siteb. Extremely important – directly affects porosity of soilc. Particle Densityi. Density of the individual pieces of sand, silt, clay paticles that make up soilii. Avg density for quartz, feldspar, and clay minerals in 2.65g/cm3d. Bulk Densityi. Density of soil including solids, pores, etc1. Always weigh dry soilii. Highly variable 1. Ranges from 0.7 g/cm3 (histisols) – 2.0 g/cm32. Low BD = goodiii. Depends on1. Texturea. Sand is denser than finer soils2. Structurea. Better structure, lower bulk density3. Management historya. Compaction = higher bulk densitye. Pore spacei. Fraction or percent of soil that is pores/voids1. %PS = 1- (BD/PD) * 100a. Use 2.65 for PD2. Ideal PS is ~50%ii. Macropores1. 005-0.1mm or lager2. Conduct excess water out of