Soil Phosphorus Availability as Measured by Displaced Soil Solutions, Calcium-Chloride Extracts, Dilute-Acid Extracts, and Labile Phosphorus1
- P. N. Soltanpour,
- Fred Adams and
- A. C. Bennett2
Five rates of Ca(OH)2 and four rates of Ca(H2PO4)2 · H2O were added in all combinations to samples of a P-deficient, low pH, sandy loam soil. The treated soil was subjected to several wetting-drying-pulverizing cycles to facilitate equilibration. Soil solutions were subsequently displaced from subsamples and analyzed; other subsamples were extracted for P with 0.01M CaCl2 and dilute acide (0.025N H2SO4 + 0.05N HCl); “labile P” was determined on subsamples from each treatment; a sorghum-sudangrass hybrid (Sorghum bicolor X S. sudanese) was grown in the greenhouse to measure P availability.
Maximum yield of test plants was obtained at about 22 µm of P in the displaced soil solution, 12 µm of P in the CaCl2 extract, 80 ppm P on soil-weight basis in dilute-acid extract, and 50 ppm of “labile P” on soil-weight basis.
The P uptake was highly correlated with the logarithm of P concentration in soil solution (r2 = 0.93) and CaCl2 extract (r2 = 0.93), logarithm of “labile P” (r2 = 0.86) and concentration of P in dilute acid extract (r2 = 0.87). All indexes were nearly equal as indicators of P availability.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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