Phosphorus fractions from a chronosequence of alluvial soils, san joaquin valley, california
1985
MEIXNER, RICHARD E. | Singer, Michael J.
This study was part of a larger effort to identify and test field and laboratory analyses useful in evaluating soil chronose-quences. We extracted five phosphorus fractions from six soil profiles formed on mixed alluvium of a chronosequence that ranges in age from 300 to 250 000 years. When expressed as a percentage of total phosphorus (PT), the content of occluded phosphorus (Poc) generally increased, and the content of nonoccluded phosphorus (Pnoc) generally decreased in B horizons. The content of calcium-bound phosphorus or apatite (PCB) tended to decrease over time in A horizons, but to change little in B horizons. The content of organically bound phosphorus (Po) did not change systematically with time.Horizon ratios of the various fractions were the most useful weathering indicators. Ratios of Pnoc for the A/B and B/C horizons had highly significant correlations with deposit age. Comparisons between horizon-ratio P percentages (PT basis) of various fractions indicated (1) that transformations from Pca to Po or Pnoc were similar in A and B horizons and (2) that rates of transformation to Poc were more rapid in B than in A horizons.The results of P fractionation for these soils formed on transported, previously weathered parent material were less clearly useful as wethering indexes than they were shown to be on soils formed by in situ weathering.
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