ABSTRACT
Calcium (Ca2+) is a divalent alkaline cation and plays many important roles in plant growth and development. When the bioavailability of Ca2+ is low, crop yield and quality can be suboptimal, depending on crop species and environmental conditions. Calcium is abundant in neutral and alkaline soils. However, calcium deficiency is most common in highly weathered acid soils, like Oxisols and Ultisols. Large areas of Oxisols and Ultisols are found in the tropics, covering about 43% of the tropics, including large areas in South America and central Africa (Thurman et al., 1980; Fageria and Baligar, 2003). According to Sanchez et al. (1983), the 580 million ha of potentially arable tropical land, with udic moisture regimes and supporting rainforest vegetation, present the largest available area for expanding the world’s agriculture frontier. These lands have no major temperature or moisture limitations and generally have topography suitable for year-round crop production. However, these soils are acidic in reaction and have low fertility (Yost et al., 1979; Goedert, 1989; Fageria and Baligar, 1997, 2003).
