Soil Basics Definitions

Soil Basics Definitions - Spring 2010 Soil Basics Page 1...

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Spring 2010 Soil Basics Page 1 Micro-Elements of the Nature and Properties of Soils 1. What is soil? Natural three-dimensional bodies used for many purposes; dynamic– its physical, chemical, and biological characteristics are constantly changing. Soils exhibit spatial variability both horizontally and vertically on the landscape. The term soil means different things to different people (think of the various functions of soil): Geologist - Weathered rock or unconsolidated deposit Civil engineer – media upon and within which to build structures and dump wastes Hydrologist – a porous media that allows fluid movement and storage Agronomist or horticulturalist– support for plant growth (also microbial biodiversity ) Pedologist – a natural body at the earth‟s surface that has formed in response to various environmental factors over time What‟s in a soil? (ideal composition for plant growth; % by volume): Inorganic solids (sand, silt, and clay minerals ~45%) Organic solids (C-based: soil organic matter, plant residues, microbial biomass; ~ 5%) Water or aqueous soil solution (~25%) Air or soil gases (~25%) 2. How is soil formed? Five soil forming factors : Parent material – pre-existing minerals, rocks, or unconsolidated material that is weathered to form soil Climate – particularly moisture and temperature, which affect weathering rates, plant growth, and additions, transformations, and losses from the soil profile Biota – microbes, plants, animals, human beings Topography or relief – slope orientation or aspect and steepness (affects moisture and temperature) Time – how long parent materials have been subjected to climate, biota, and topography The five factors create soil by acting through four soil forming processes: Additions to the ground or soil surface Removals from the soil Transformations or weathering reactions within the soil Transfers or translocations (vertical and horizontal) within the soil profile Once formed, soil can be classified into a taxonomy that includes twelve SOIL ORDERS based on their observable and measured properties and horizons. Classification of soil: Order, Suborder, Great Group, Subgroup, Family, Series (most general) (most specific) Master soil horizons : created in response to pedogenesis and indicative of soil forming factors. O Surface horizon composed mostly of organic matter A Uppermost horizon, composed mostly of mineral material but rich in organic matter E Subsurface elluvial (leached) horizon from which clays, Fe/Al oxides have been removed; lighter in color than the A horizon B Subsurface zone of accumulation (clay, organic matter, Fe/Al oxides) and/or structural alteration C Geologic materials, including partially weathered bedrock, little pedogenesis R Hard Bedrock 3. What are some of the important physical properties of soil?
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Soil Basics Definitions - Spring 2010 Soil Basics Page 1...

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