Calcium (Ca) is usually supplied in sufficient quantities by liming if appropriate liming materials are chosen (see Soil Acidity, pH, and Liming in the next section). If soil pH is high and Ca is needed, it can be supplied without affecting pH by applying calcium sulfate (gypsum) which contains 19%-23% Ca. Small amounts can also be applied as calcium nitrate fertilizer (19% Ca) or superphosphate (18%-21% Ca). See Table 5.