INFLUENCE OF PH ON GROWTH AND NUTRIENT-UPTAKE BY CROP SPECIES IN AN OXISOL

Crop growth in Oxisols is known to be limited by high soil acidity and low levels of basic cations. Five greenhouse experiments were conduct ed to evaluate the effects of soil pH on the growth and nutrient uptak e of upland rice (Oryza sativa L.), wheat (Triticum aestivum L.), corn (Zea mays L.), common bean (Phaseolus vulgaris L.), and cowpea (Vigna unguiculata L. Walp.). Six levels of soil pH (4.1, 4.7, 5.3, 5.9, 6.6 , and 7.0) were achieved by addition of various levels of CaCO3. Crop species responded differently to pH, reflecting the genetic diversity among species. Higher dry matter accumulation in roots and tops of ric e, corn, and cowpea was observed at acidic pH ranges indicating that t hese species are tolerant to soil acidity. However, increasing soil pH enhanced dry matter accumulation in roots and tops of wheat and commo n bean, reflecting their intolerance to soil acidity. In all of the cr op species, uptake of calcium (Ca) and magnesium (Mg) decreased with a decrease in soil pH. Overall uptake of zinc (Zn), manganese (Mn), and iron (Fe) in all species increase with a decrease in soil pH. Higher pH in an Oxisol might induce micronutrient deficiencies; therefore, on e has to avoid overliming. In general, increasing soil pH decreased th e uptake of nitrogen (N), phosphorus (P), and potassium (K) in rice, b ut uptake of these elements increased in wheat, corn, and common bean. In order to achieve the full genetic potential of any given species o n an Oxisol, one needs to consider the species tolerance to soil acidi ty and its nutrient demand.