Calcium Research Paper

1095 Words 5 Pages
1. Calcium is the fifth common element in the earth’s crust, and is found predominantly in feldspar, calcite, dolomite, and apatite, as a primary and secondary mineral. Calcium is found in lime stone but is also added as lime and in fertilizers. However, Calcium is not added as the soil is insufficient in Calcium, but to increase the pH. Calcium is a macro-nutrient which is essential in plant growth, the functioning of root tips, and is a main constituent in the cell wall. The amount of Calcium in soil will depend on the parent material and extent of weathering. Immobility of Calcium will be seen at the growing tips of the plant. Plants require a continuous supply of Calcium; however, inefficient aeration and temperature will affect this. Calcium …show more content…
There are two main processes as to how surface charges are created: isomophous substitution and dissociation of H+/OH-. An Isomophous substitution creates permanent charges that occur within tetrahedral and octahedral structural units in the clay minerals, via cation substitution. Cations are exchanged with cations of similar sizes but difference valencies. For example, where Al3+ is substituted by Si4+; this creates a net negative charge on one of the oxygen’s, because of the unpaired electron. Dissociation of H+/OH- is pH dependant and creates variable charges. These are created from the dissociation of the hydrogen ion in organic matter, and hydrogen ions being added and removed of the alcohol (OH) group on mineral surfaces. The amounts of charge changes due to the pH, as the concentration of hydrogen and hydroxide ions determine the pH. This relates to soil solution acidity. How acidic the soil is shown by the concentration of hydrogen ion there are within the solution. Therefore, the higher concentration of OH- will have a higher pH- more alkaline. There are two processes that contribute to soil …show more content…
Soil surfaces are created from isomophous substitution and the dissociation of H+/OH- (as explained above). A net negative charge can be created, which is the common charge amongst NZ soils. Opposite charges attract, therefore, cations will be attracted to the soil surface, not anions (like charges repel). This is electrostatic attraction, which will cause cation exchange. Cation exchange is the exchange between the cations held on the soil colloid surface and the soil solution. Since Calcium is a cation (Ca2+), this will be attracted to the anions. Furthermore, because Calcium is a divalent cation, it will be held more strongly than a monovalent cation (i.e. Na+). A change in the equilibrium between the soil surface and solution will cause exchange reactions. This can be referred to as a Le Chatelier’s Principle: if a change occurs to the equilibrium, the equilibrium will shift to counteract the effect. For example, the intake of Ca2+ onto the soil surface will cause H+ to be released into the soil solution so equilibrium is established again. As stated above, Calcium is a divalent cation, therefore, it is more strongly held than a monovalent cation. Therefore, being attracted to negative surfaces, the diffuse layer will be more compact, since the higher the charge, the more attraction. There will be a higher concentration of Ca2+ at the colloid surface, which decreases in concentration down the soil profile towards the bulk solution, because of the attraction and

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