Rice varieties IRS and Chontalpa 16 growing in two Ultisols with periodic overhead irrigation were quite tolerant to acidity producing around 80% of maximum yield at pH 4.8 and 30% Al saturation of the soils cation exchange capacity, a level common in Ultisols. However, maximum yields were obtained at pH 5.5 when no exchangeable Al was present in the soil. The Ca content of the leaves of both rice varieties decreased with decreasing pH and increasing Al saturation of the soils exchange

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... Soil acidity factors in an Oxisol did not affect yields of the IRS variety, even at pH 4.5.