ABSTRACT
Calcium (Ca) and magnesium (Mg) are essential plant nutrients. Along with sulfur, they are sometimes referred to as secondary elements, which are required by plants in large amounts for normal growth and development. Calcium and magnesium deficiencies are very common in Oxisols, Ultisols, Alfisols, and Inceptisols on which upland rice is grown (Clark 1982; Fageria and Souza 1991; Fageria 2000; Fageria and Baligar 2008). Data in Table 5.1 show the response of upland rice to soil pH. The dry matter yield of straw, grain yield, panicle density, and 1000-grain weight were significantly increased with increase in soil pH or addition of lime (Ca2+ and Mg2+). With a change in pH or the addition of lime, the variability was 99% in straw yield, 91% in grain yield, and 94% in panicle density. Calcium is usually the predominant soil cation and is present in relatively large amounts, especially on alkaline soils. Ca2+ is a nontoxic mineral nutrient, even in high concentrations, and is very effective in detoxifying high concentrations of other mineral elements in plants (Marschner 1995).
