SPADA Draft Documents

contain more characteristics of the bedrock below or the displaced material deposited at 66 the site. 67 ( d ) Cation exchange capacity (CEC) .—The sum total of exchangeable cations that a 68 soil can adsorb. Sometimes called total-exchange capacity, base-exchange capacity or 69 cation-adsorption capacity. CEC is expressed in centimoles of charge per kilogram 70 (cmolc/kg) of soil (or of other adsorbing material, such as clay). 71 ( e ) Clay .—A soil consisting of particles <0.002 mm in diameter. Clay is negatively 72 charged and has capacity for water retention. 73 ( f ) Clay mineral .—Naturally occurring inorganic material (usually crystalline) found 74 in soils and other earthy deposits, the particles being of clay size. 75 ( g ) E horizon .—Light colored mineral horizon where most of the organic matter and 76 smaller minerals have eluviated or leached out of the layer. 77 ( h ) Fine sand .—Comprised of particles in diameter range of 0.2-0.02 mm. Made of 78 weathered primary rock minerals and particles that do not pack together easily. Air 79 enters easily and water flows through fine sand rapidly. 80 ( i ) Fulvic acid.— A term of varied usage but usually referring to the mixture of 81 organic substances remaining in solution upon acidification of a dilute alkali extract from 82 the soil. 83 ( j ) Humic acid .—A mixture of variable or indefinite composition of dark organic 84 substances, precipitated upon acidification of a dilute alkali extract from soil. 85 ( k ) Humin .—The fraction of the soil organic matter that is not dissolved upon 86 extraction of the soil with dilute alkali. 87

Draft Version 16

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