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This article in SSSAJ

  1. Vol. 56 No. 3, p. 849-856
    Received: Nov 28, 1990

    * Corresponding author(s):


Phosphorus Distribution in Loessial Fragiudalfs as Affected by Relief

  1. R. E. Switzer  and
  2. D. E. Pettry
  1. Department of Agronomy, Mississippi State Univ., Mississippi State, MS 39762



Topographic effects on P form and distribution were determined in three loessial toposequences. Loring soils (fine-silty, mixed, thermic Typic Fragiudalfs) were sampled in the top- and midslope positions. Slopes ranged from 1 to 2% in the topslope and 9.5 to 13% in the midslope pedons. Phosphorus distribution reflected changes in topographic position and the influence of fragipan horizons (Btx) in the pedons. Nonoccluded, occluded, organic, and total P decreased while Ca-P increased as slope increased. Nonoccluded exceeded occluded P in the topslope Bt horizons, while occluded P dominated in the Btx horizons. Occluded P dominated midslope Bt and Btx horizons. Results suggest a loss of P and a reduction in weathering intensity as slope increased. Significant correlations were found between nonoccluded and occluded P and clay, dithionite- and oxalate-extractable Fe, and total Fe while Ca-P and organic P were correlated with pH and base saturation in the topslope pedons. In the midslope pedons, significant correlations were found between occluded P and clay and dithionite-extractable Fe while Ca-P and organic P were correlated with pH, base saturation, and organic matter. Maximum clay and total P occurred in similar Bt horizons in all topslope pedons. Changes in P distribution occurred into and below the Btx horizons, suggesting these changes occurred prior to and during fragipan formation.

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