Expert: Mick Bridge - 4/19/2005

Question
Hi Mick,

I have treid using dolomite to raise the pH of soil growing common Bermuda grass. I would like to know more about how dolomite could raise the soil pH.

Another question is do you know whether fungicide Bayleton and insecticide carbaryl consist of heavy metals like Cd, Cr, Cu, Ni, Pb and Zn, etc.?

Thanks!

Yours sincerely,
raymond

Answer
Dolomite is a mixed magnesium / calcium carbonate rock. It contains about 10%+ of Magnesium. Carbonates are slightly alkaline so addition of CaCO3 or MgCO3 to soil makes it more alkaline (higher pH). Lime (calcium hydroxide) is the most alkaline chemical it is useful to apply to soil, hence "liming the soil". However it is very caustic so dangerous to handle, whereas carbonates are completely safe. Some plants don't like too much calcium, but they don't mind Mg which is an essential plant micronutrient. Chlorophyll, the green plant pigment essential for photosynthesis contains Mg. So dolomite is safer than limestone to some plants.
The problem is that the buffering capacity of soil is very high. This means that a lot of chemical has to be applied to change pH significantly. For example, about 9 oz per square yard (300g/m2) of dolomite has to be put on to raise pH by 0.5 units e.g. 6 to 6.5. The more finely ground the dolomite the quicker it will work, but heavy rain may wash it away in sandy soils so it will need applying again. Dolomite grit applied in a larger quantity may last longer but will work slower.

Re Bayleton and Carbaryl. These are organic compounds - in the chemistry sense, not the modern one of "natural". This means they contain organic carbon. This applies to the vast majority of pesticides. The only products containing heavy metals are some fungicides consisting of copper salts and some others containing Manganese and Zinc in organic polymers. Ferrous (iron) sulphate is used for moss control on lawns. In some countries (including, I believe the US), some arsenic salts are still used as defoliants in cotton but most countries banned these products many  years ago.