Phosphorus Sorption and Uptake from Sri Lankan Alfisols
- R. A. Morris ,
- R. R. Sattell and
- N. W. Christensen
Soil organic P as well as inorganic P quantity and capacity factors have been identified as P availability determinants in tropical soils. The effects of these factors on P uptake from 12 Sri Lankan Alfisols were determined. For the analysis, a P quantity variable (Q, µg g−1 soil) was P extracted by 0.5 M NaHCO3 (16-h shaking). The tangential buffer capacity inverse (× 103), computed at points on P sorption isotherms corresponding to Q, was the capacity variable [B, µg solution P × 103 g−1 solution/(µg sorbed P g−1 soil)]. Phosphorus extracted by 0.1 M NaOH (16-h shaking) after removal of labile P was a moderately labile organic P variable (Op, µg g−1 soil). Phosphorus uptake by foxtail millet [Setaria italica (L.)] was determined from Neubauer pots. A regression equation indicated significant influences by Q, B, and Op on P uptake. The effect of Op was through an interaction with Q. Moreover, applied inorganic P increased moderately labile organic P by only 11% but labile inorganic P by 255%. The significant interaction was evidence that applied inorganic P increased uptake from the labile inorganic P pool in soils with high NaOH-extractable organic P relative to uptake from soils with low NaOH-extractable organic P. The interaction between Q and Op was consistent with three alternative hypotheses regarding the contribution of organic P to soil P status. The first derivative of the regression equation with respect to Q was used to examine a soil × applied P interaction in the uptake data. Variables from the first derivative explained about two- thirds of the soil × applied P interaction of P uptake from the Neubauer pots, evidence that P sorption properties as well as Op differences among the 12 soils influenced P availability.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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