Lime-magnesia ratios in dolomitic limestones as influencing solution and soil reactions

A study was made to determine the influence that calcium-magnesium ratios exert upon the behavior of dolomites toward carbonated water. The higher proportions of calcium the greater were the alkalinities of the extracts and the more quickly were equilibria obtained in initial carbonated water suspensions. The Ca:Mg ratios determined the proportions in which the two elements are initially and progressively available for absorption in the soil system. When subjected to repeated treatments with carbonated water, the dolomites at first disintegrated through the dissolving out of CaCO3 and CaCO3-MgCO3; but after the removal of the CaCO3 excess, the dolomite residues yielded solutions in a constant Ca:Mg ratio of 1:1. Additions of CaCO3 and MgCO3 to dolomite suspensions in carbonated water were found to be reciprocally repressive upon solubility and mutually protective to the solid-phase dolomite. It is pointed out that the Ca:Mg ratio of a solid dolomite, or that of its carbonated-water solution, is not an index to the proportions of calcium and magnesium that are to be found in the soil solution after the dolomite has become a part of the soil system. The addition of economic amounts of dolomite resulted in percolates that contained less calcium and more magnesium than did those from the untreated soil. It was shown that acids engendered in a soil-dolomite medium will combine preferentially with magnesium to enhance the magnesium outgo from fallow soil, or to enrich the contents of growing plants. It was pointed out that dolomites exert a protective action upon the hydrolysis of both native calcium and native potassium, the latter function being in common with that of high-calcic limestone. It was also pointed out that periodic outgo of calcium and magnesium from a dolomite addition differs from that derived from its calcined oxides. The correlation of solubility and acid-reaction studies with lysimeter findings apparently justifies the conclusion that, under humid conditions, additions of dolomitic limestone cannot produce a toxic condition from an accumulation of magnesium per se, since the outgo of added magnesium exceeds that of added calcium.