SIGNIFICANCE OF SILICA IN THE LOSS OF MAGNESIUM FROM IRRIGATION WATERS

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Abstract
The preci-pitations of Ca and Mg from soil solutions with evapotranspiration tend to occur in proportion to the concentrations of the 2 ions in the irrigation water. Because of the presence of HCO3 in natural waters, the Ca is precipitated as CaCO3, but the loss of Mg is in the form of silicates. The precipitation of Mg-silicates is dependent upon the ioni-zation of SiO2 which occurs as soil solutions become alkaline with the formation of CaCO3 and the escape from the soil of the CO2 produced by this reaction and by that resulting from biological oxidations. The suitability of soils for crop production declines with increases in alkalinity and Na percentages. The data are discussed in terms of water-quality appraisals. The occurrence of SiO2 in natural waters and factors that influence its concentration are illustrated.