Volume 13 Part 2 Article 44: Dolomite Upsets the Carbon Dioxide Balance

Volume 13 Part 2 Article 44
Year 1991
Title: Dolomite Upsets the Carbon Dioxide Balance
Author: R.H. Kurtzman Jr.


For years, mushroom growers have been warned to avoid dolomite in their casing. Dolomite delays the onset of fruiting and decreases yields. Generally, magnesium is said to be toxic. Chemical experiments suggest a somewhat different explanation. When an aqueous slurry of CaCO3 was exposed to CC2, Ca(HCO3)- and H2CC3 were quickly formed. Magnesium carbonate formed Mg(HCO3)2 and H2CO3 slowly and the resulting mixture was unstable. In 100% CO2 at one atm, Ca(HC03)2 solutions remained at pH 6.09 indefinitely, while Mg(HCO3)2 solutions remained at pH 7.21. Bom mixtures are less stable in ordinary atmospheric conditions: In 24 hours, the calcium solution rose to about pH 6.5 while the magnesium rose to pH 8 or higher. Thus calcium slurry held 13 to 32 times more bicarbonate than magnesium. Magnesium tends to maintain the bed at a much higher pH than calcium. In a stream of carbon dioxide, Ca(HCO3)2 is soluble in water to approximately 0.625 g/1 and Mg(HCO3)2 to approximately 2.5 g/L. Ionic solubilities have a proportional effect on the conductivity of casing ana compost. Conductivity, CC2 and pH are important factors in fruiting and yield, those factors rather than direct cellular toxicity may make magnesium harmful.

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