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Cation-exchange capacity (CEC) is a measure of how many cations can be retained on soil particle surfaces. [1] Negative charges on the surfaces of soil particles bind positively-charged atoms or molecules (cations), but allow these to exchange with other positively charged particles in the surrounding soil water. [ 2 ]
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.
Nutrient cations, including potassium and many micronutrients, are held in relatively strong bonds with the negatively charged portions of the soil in a process known as cation exchange. Phosphorus is a primary factor of soil fertility as it is an element of plant nutrients in the soil.
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 cations (H + ) that will combine with 100 grams dry weight of soil and whose measure is one ...
4) cation produced by urea hydrolysis which is a strongly sorbing cation exchanges with the weakly sorbing Na + cation from the soil structure and Na + is released into water. Thus alkali soils adsorb / consume more urea compared to other soils. To reclaim the soils completely one needs prohibitively high doses of amendments.
Soil sieve nests with dry soil aggregates after removal from a laboratory drying oven. Soil aggregate stability is a measure of the ability of soil aggregates—soil particles that bind together—to resist breaking apart when exposed to external forces such as water erosion and wind erosion, shrinking and swelling processes, and tillage.
Idealized image of cation-exchange resin performing water softening. It shows sodium ions being released by the resin, and replaced with calcium ions captured from water. Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water.
Thermoeconomics is based on the proposition that the role of energy in biological evolution should be defined and understood not through the second law of thermodynamics but in terms of such economic criteria as productivity, efficiency, and especially the costs and benefits (or profitability) of the various mechanisms for capturing and utilizing available energy to build biomass and do work.