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Environmental GeoscienceHonours ProjectsThe effect of magnesium hydroxide on the physical properties of soilGemma Nicol The effect of magnesium hydroxide, Mg(OH)2 on the physical properties of soil is relatively unknown. Few studies have been completed on Mg2+, and even fewer have been completed on the effect of Mg(OH)2, leaving an opening in the literature that is prolific with studies on sodium and calcium. The possibility of using waste water that contains a high concentration of Mg(OH)2 demanded attention be directed toward finding out the possible deleterious effects that Mg(OH)2 may have on the soil. In Part A, pure clays of illite, bentonite and kaolinite were treated with NaCl, CaCl2, MgCl2 or Mg(OH)2 to a homoionic state. The physical response of the clays to changes in pH and EC were the most prominent. Soil was then sampled from the A horizon of the agricultural reserve at La Trobe University and subjected to various treatments. The first of these treatments (Part B) involved measuring the change in hydraulic conductivity of intact soil cores with the application of NaOH, CaCl2 or MgCl2. Subsequent measurements of soil physical properties showed that as pH increased there was a negative change to soil strength and dispersion. Next, Part C involved the use of waste water collected from either Mars Confectionery in Ballarat, or Bonlac Foods in Cobden and leaching the soil columns with various pore volumes. Subsequent measurements of soil strength and dispersion showed insignificant affects of Mg(OH)2 on the physical properties of the soil. This conclusion was further supported by experimental results of Part D, establishing the need to extend this experiment into a field trial using much greater pore volumes, similar to the volumes of water that would be used for irrigation. Overall, the major effect of applying Mg(OH)2 on the physical properties ofsoil is likely to be due to an increase in soil pH. Increasing soil pH increased dispersion, due to the elimination of edge-to-face particle interaction. The effect of Mg2+ as an exchangeable cation is only likely to be evident when the Mg:Ca ratio exceeds some critical value determined by the electrolyte concentration of the soil solution. Content Approved by: Head of Environmental Geoscience
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