Transcript Lecture 2
Anyone who did not attend Lecture I, see me after class for materials and course basics Soil Basics Arcanum Mysterious knowledge known only to the initiated ? What is Soil? What is Soil? It is not Dirt What is Soil? …unconsolidated surficial material Short-sighted Engineer, 1985 What is Soil? A dynamic natural body composed of mineral and organic materials and living forms in which plants grow. The collection of natural bodies occupying parts of the earth’s surface that support plants and have varying properties due to the integrated effects of climate and life acting upon geologic materials, mediated by relief (topography) and time Brady and Weil, 2000 What is Soil? Agronomist Forester Horticulturalist Engineer Environmentalist Ecologist Functions of Soil Medium for plant growth Regulator of water supplies Recycler of raw materials Habitat for soil organisms Engineering medium Fundamental Components of Soil Idealized Surface Soil Voids Avenues Storage Distribution Movement Solids Interactive Media Minerals Organic matter Reactivity Components of Soil Gases Oxygen: Carbon Dioxide: ~ 25% Atmosphere 21% 0.038% Soil Atmosphere 5-10% 0.3-3% Microorganisms tend to reduce oxygen and enrich carbon dioxide Components of Soil Liquid ~ 25% Dissolved and Suspended Constituents Nutrients Metals Salts Acids/Bases Organic Compounds Contaminants Gases Solid Phase Components of Soil Mineral + Organic ~ 50% Solid soil particles and organic matter Organic: decomposed plant and animal material Mineral: Sands, silts, clays, oxides (Al and Fe) • reactivity • Water movement/retention Organic Organic Matter Mineral Soil < 20% O.M. 5% Organic Soil > 20% O.M. >50% Vegetative Influences Forested Deciduous Coniferous Grasses Organic Matter Generalizations • Soil color – the darker the color, the more OM. • Soil structure – cementing agents, fibers. • Soil nutrients –organically derived (P, S, N, Ca, Mg, K). • Energy sources – energy for soil organisms. • Soil Water – increases water holding capacity • Soil reactivity – increases chemical reactivity of soils Mineral Components of Soil Mineral ~ 45% Rocks, stones, gravel, particles, aggregates Particles: Rocks primary minerals (quartz, feldspars) secondary minerals (clays, oxides) Primary Minerals Secondary Minerals Can be highly reactive Soil Formation and Morphology Basics Processes Additions Losses Translocations Transformations Soil as a Natural Body Differentiation Additions Losses Translocations Parent Material Transformations Bedrock Bedrock The Essentials of Soils Soil Profile – 2D representation of a vertical section of soil from the surface to its deepest layers. Differentiation of layers Is highly variable. Soil Profile Soil Horizons Roughly parallel layers in the soil with varying composition and properties Soil Master Horizons Master Horizons A horizon [ The A Horizon • topsoil/plow layer. • Accumulates organic material • Often darker than soil below. • high in plant roots, biotic activity • Zone of gas and water exchange A horizon A horizon Master Horizons A horizon B horizon [ The B Horizon - Accumulates material transported from above, or forms in place. (translocation, transformation) - Zone of Illuviation (translocation). - clays, O.M., Fe/Al oxides, salts • good soil structure • Strong color development • Potentially high reactivity B horizon Master Horizons A horizon B horizon C horizon [ The C horizon -Weakly altered by soil forming processes. -Closely resembles parent material C horizon Master Horizons A horizon B horizon C horizon E horizon The E horizon - Zone of Eluviation A horizon Eluviation = exit Illuviation = into E horizon •Organic matter •Clay •Carbonates •Fe, Al oxides •color (Elluvial) B horizon (Illuvial) Master Horizons A horizon E horizon B horizon C horizon R Horizon Florida? The R Horizon limestone R horizon The O Horizon • • Surface Horizon Organic horizon Non-mineral dark-colored • Often called peat, muck • Some are very fertile, valuable • In some countries, O horizon used as fuel. O Horizon Soil Horizons O horizon O horizon Master Horizons A horizon A horizon E horizon B E horizon horizon C horizon B horizon R Horizon O organic A topsoil E elluvial B developed C parent material R bedrock Soil Profiles Delineating Soil Horizons Criteria for Characterizing Soil Horizons Color Texture Density Structure Organic matter Mineralogy Chemistry Soil Physical Properties Soil Color Soil Color Determinants • • • • Mineralogy of the soil/parent material Relative amount of organic matter or iron Hydrology of the soil Oxygen status Soil Color Determination Munsell Soil Color Hue dominant spectral color; related to the wavelength of light. Related to the proportions of red to yellow. Value related to total amount of light reflected. Chroma measure of the strength of spectral color Soil Color Hue = 10 YR Value = 6 Chroma = 3 Munsell Color 10 YR 6/3 Summary Hue dictates dominant spectral color for a given page. Low value indicates dark soil colors. (O.M.?) High chroma indicates strong color expression 10YR 3/6 Communication Water table depth Oxygen status Development decisions Criteria for Characterizing Horizons Color Texture Density Structure Organic matter Mineralogy Chemistry