Calcium carbonate, its sister chemical magnesium carbonate and the combination of the two (dolomite) may cause problems for the gardener.
Calcium carbonate is a compound which contains calcium and carbonate. This compound occurs naturally and is found in limestone, shells, chalk and marble.
Magnesium carbonate is a compound (also called magnesite) formed when magnesium is combined with carbonate. It occurs naturally and is an essential part of dolomitic limestone and dolomite. It often occurs naturally in aquifer water (well water) and is one of the substances that make “hard water.”
Dolomite is limestone containing equal amounts of magnesium carbonate and calcium carbonate.
Soils in deserts, arid and semi-arid regions tend to have naturally high pH levels. Irrigating with water high in magnesium carbonate or calcium carbonate raises the pH of the soil even higher, and makes it more difficult for even plants that are tolerant to higher pH levels to cope.
Other areas in North America and elsewhere also have high pH levels, and irrigation water from wells may be high in magnesium or calcium carbonate.
Caliche (or hardpan) is formed when calcium and magnesium are leached from the topsoil and percolate down into the next layer of soil, or moves up through the soil through capillary action. Caliche can be trouble for plants because the impermeable nature of caliche keeps water from draining (it acts as a sort of bowl). This can keep the roots from getting enough oxygen. Caliche can cause other problems with plants too.
