Comparison of resin beads and resin membranes for extracting soil phosphate |
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Authors: | M L V Fernandes and G P Warren |
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Affiliation: | (1) Seccão Autónoma de Quimica Agricola, Instituto Superior de Agronomia, Tapada da Ajuda, 1399 Lisboa Codex, Portugal;(2) Department of Soil Science, University of Reading, Whiteknights, P.O. Box 233, RG3 2DW Reading, UK |
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Abstract: | Six Portuguese soils of varying P sorption capacity were incubated aerobically at 30° C without and with added P in order to give 0.1.mg P L–1 in the soil solution. Two methods of measuring extractable P were compared: (i) mixed-bed cation-anion-resin beads in bags and (ii) a simpler method with anion-resin membrane only. The bag method extracted about twice and 1.5 times as much as the strip method, respectively, without and with added P. The relationships were much closer after one extraction for 2 hours (r = 0.982, p < 0.01) instead of the cumulative extraction of 24 hours (r = 0.635,p > 0.05.). P recovery after incubation was inversely related to some soil properties as organic matter, buffer capacity, selective dissolution Al forms (Alox and Ald) and P sorption. It is suggested that the simpler resin membrane method is more adequate to assess P for many studies of P reaction with soil. A simpler incubation method was tried, consisting of incubation as a soil suspension in water at a high temperature (50° C). The results suggested that this method gave similar results to aerobic incubation, with the advantage that there was no need to measure the required and final water contents of incubated soil. |
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Keywords: | aerobic incubation cation-anion-exchange resin phosphorus resin beads resin membranes suspension incubation |
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