Plant Tolerance of Low Soil pH, Soil Aluminum, and Soil Manganese

Some plants are more able than others to grow on soils with low pH. This interesting ability was not well recognized until the past 20 years or so, and it still is not fully understood. Crop tolerance of low soil pH has become extremely important in the agricultural development of the humid tropics because so many of those soils have low pH (Kamprath and Foy 1985, Salinas and Sanchez 1981, Maranville 1992). In Hawaii, this tolerance can be important because there are extensive areas of soils with low calcium (Ca) and considerable areas with soil toxicity due to high levels of aluminum (Al) and manganese (Mn) (reviewed in Yost and Evensen 1994). One reason sugarcane was successful in Hawaii may be related to its considerable tolerance of low Ca and high Al (ibid.). Pineapple is notable for its tolerance of and, indeed, requirement for low soil pH. Hawaii is an example of a place where crops have been selected to fit soil conditions rather than amending soils to fit crops, which is the traditional method of soil management in many temperate climates. This chapter describes some examples of crop tolerance of factors related to low soil pH—primarily, high levels of toxic Al and Mn. These examples illustrate the impressive differences among plants in adapting to and tolerating low pH in soils of the humid tropics. Some of the first research identifying and quantifying crop tolerance of soils with low pH has come from the tropics (Spain et al. 1975, Silva 1976; see Figure 11-1). Identifying and understanding crop tolerance Chapter 11