Interaction of Phosphorus Rates and Soil pH on Soybean Yield and Soil Solution Composition of Two Phosphorus-Sufficient Ultisols1
- J. F. Adams,
- Fred Adams and
- J. W. Odom2
Because growers continue to use phosphorus (P) fertilizer on soils that test high in available P, two field experiments were conducted to determine what nutritional problem, if any, would develop in soybeans (Glycine max L.) when high levels of P were established on Ultisols. Soil pH levels, ranging from 5.0 to > 7.0, were established by differential limiting; five P rates as concentrated superphosphate were superimposed on the pH levels. Zinc (Zn) deficiency was induced by high P rates and high pH, and the magnitude of yield reduction corresponded with the intensity of deficiency symptoms on foliage. Leaf Zn, acid-extractable soil Zn, and soil solution Zn were poor indicators of Zn deficiency. The ratio of P/Zn in leaves was a fair indicator in one soil and a poor one in the other, possibly because of differences in availability of subsoil Zn. Soil solution Zn, which ranged between 0.1 and 5.1 µM, was affected by pH but not P level. Soil solution P, which ranged between 5 and 230 µM, was affected primarily by P rates. Both SO4 and Si concentrations in soil solutions were increased by increasing P rates. Calculated ion activity products for Ca5OH(PO4)3 showed numerous soil solutions to be supersaturated with respect to hydroxyapatite.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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