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Cation exchange at the surface of a soil particle. Cation-exchange capacity is defined as the amount of positive charge that can be exchanged per mass of soil, usually measured in cmol c /kg. Some texts use the older, equivalent units me/100g or meq/100g.
Soil properties that can be measured quantitatively are used in this classification system – they include: depth, moisture, temperature, texture, structure, cation exchange capacity, base saturation, clay mineralogy, organic matter content and salt content. There are 12 soil orders (the top hierarchical level) in soil taxonomy.
Soil mineral components belonging to a given textural class may thus share properties linked to their specific surface area (e.g. moisture retention) but not those linked to their chemical composition (e.g. cation exchange capacity). Soil components larger than 2.0 mm (0.079 in) are classed as rock and gravel and are removed before determining ...
The cation exchange principle was discovered by Thomas Way and John Bennet Lawes at Rothamsted Experimental Station in the 19th century. In 1892 Oscar Loew observed that both calcium and magnesium can be toxic to plants when there is an excess of one and a deficiency of the other, thus suggesting there may be an optimal Ca:Mg ratio.
Cation exchange capacity is the soil's ability to remove cations from the soil water solution and sequester those to be exchanged later as the plant roots release hydrogen ions to the solution. [103] CEC is the amount of exchangeable hydrogen cation (H + ) that will combine with 100 grams dry weight of soil and whose measure is one ...
The clay soils containing montmorillonite or smectite (swelling clays) are more subject to alkalinity problems than illite or kaolinite clay soils. The reason is that the former types of clay have larger specific surface areas (i.e. the surface area of the soil particles divided by their volume) and higher cation exchange capacity (CEC). Note:
The sodium adsorption ratio (SAR) is an irrigation water quality parameter used in the management of sodium-affected soils.It is an indicator of the suitability of water for use in agricultural irrigation, as determined from the concentrations of the main alkaline and earth alkaline cations present in the water.
A simplified version of the Emerson soil dispersion test [3] can be completed in the field on a 20-minute to two-hour timescale. Laboratory tests used to diagnose a soil as dispersive focus on the cation exchange capacity of a soil sample and its cation breakdown. Soil cations are dominated by Ca 2+, Mg 2+, K +, and Na +, as well as H + in ...