Biology Question #167

Mary Phipps, a 50 year old female from the Internet asks on April 27, 2000,

Is calcium carbonate (ground limestone) biodegradable? Will it break down during composting? I want to compost manure and wood shavings and have access to large amounts of calcium carbonate (ground limestone, CaCO3). Will the fungi and bacteria active in composting be able to break down the carbonate in the ground limestone and use it as a source of carbon?

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The answer

Barry Shell answered on April 27, 2000

Probably not. Inorganic carbon in the form of limestone is not as good for compost as organic carbon in the form of vegetable matter. Ground limestone is not really organic, at least not in the way I define it, which is as carbon created as a result of primary (plant) or secondary (animal) production. Limestone is good for compost in small amounts, but as a neutralizer of acid, rather than as a source of carbon. CaCO3 reacts with water and CO2 to produce calcium and carbonate ions. By adding large amounts of limestone, you would end up with an alkaline mix which could be inhospitable to your bacteria and worms. The best source of organic carbon for compost is grass clippings, leaves, kitchen waste and other organic matter.

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