Calcium (Ca) is usually supplied in sufficient quantities by liming if appropriate liming materials are chosen (see "Soil pH and Liming"). If soil pH is high and Ca is needed, small amounts can be applied as calcium nitrate fertilizer (15% N, 19% Ca). Ca can also be supplied without affecting pH by applying calcium sulfate (gypsum) which contains 22% Ca or superphosphate (14% to 20% Ca). See Table 6.