PHOSPHORUS NUTRITION OF PLANTS INFLUENCED BY MANGANESE AND ALUMINUM UPTAKE FROM AN OXISOL

Abstract

The effect of changes in soil pH on the plant availability of soil P and the interaction between Mn and Al accumulation and P response of tomato and corn plants were evaluated. Yield response of tomato plants grown in pots to the level of P in soils was affected by soil pH. Plants in soils with pH values of 6.3, 6.7, or 7.2 produced maximum growth if the soil solution P level was adjusted to 0.2 ppm. At lower soil pH values, 5.1, 5.3 and 5.7, yield increased up to 0.8 ppm, the highest solution P level employed. This yield, nevertheless, was still below that for higher pH values. By contrast, the effect of P fertilizer on corn hardly varied at different pH levels. Evidence of Mn and/or Al toxicity on tomatoes is presented. Apparent toxocity was lessened by high levels of P. A threshold toxicity level of 450 ppm Mn in tomato tops is proposed. Soil P solubility as measured by phosphate sorption isotherms did not change over a range of soil pH between 5.1 and 7.2.