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This article in SSSAJ

  1. Vol. 65 No. 1, p. 139-146
     
    Received: June 4, 1999


    * Corresponding author(s): rsyost@hawaii.edu
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doi:10.2136/sssaj2001.651139x

Soil Aggregate Size Affects Phosphorus Desorption from Highly Weathered Soils and Plant Growth

  1. X. Wanga,
  2. R.S. Yost *a and
  3. B.A. Linquistb
  1. a Dep. of Tropical Plant and Soil Sciences, Univ. of Hawaii, Honolulu, HI, 96822
    b International Rice Research Institute, P.O. Box 933, Manila 1099, Philippines

Abstract

Because plant absorption of P depends on the desorption of P from soil, understanding P desorption from soils may improve the precision of P diagnosis and fertilization recommendations. Many soils with high P retention due to high levels of Fe and Al are also highly aggregated. Extractable P is sometimes higher on larger size aggregates, which will probably result in increased P release from aggregates. The effects of aggregate size on P availability of three highly weathered soils were quantified with a column-leaching study and a pot experiment. Phosphorus desorption by leaching from small aggregates was greater than that from large aggregates when P had been added to the bulk soil (Kapaa and Leilehua soils) and a mixture of different-sized aggregates (Leilehua soil). When aggregates were separated and then P added, however, P desorption was greater from large aggregates (4–6 mm) than from small aggregates (<0.5 mm). Conformity of the P desorption data to the parabolic diffusion and expanded Elovich equations suggests that P desorption is probably controlled by diffusion processes. A pot experiment showed that total P in lettuce (Lactuca sativa L.) and soybean [Glycine max (L.) Merr.] shoots, and the root dry weights of plants grown in the large aggregates (2–6 mm) were higher than for plants grown in the small aggregates (<0.5 mm) after equal amounts of P were added to the separated aggregate fractions. Increased P uptake with increased aggregate size was attributed to increased P release from aggregates because of reduced P fixation. The results suggest that soil management that favors soil aggregation may, in some cases, increase availability of applied P. Perhaps the distribution of soil aggregates should be considered in making P management decisions.

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Copyright © 2001. Soil Science SocietyPublished in Soil Sci. Soc. Am. J.65:139–146.