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This article in SSSAJ

  1. Vol. 61 No. 1, p. 160-166
     
    Received: Aug 31, 1995
    Published: Jan, 1997


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doi:10.2136/sssaj1997.03615995006100010024x

Aggregate Size Effects on the Sorption and Release of Phosphorus in an Ultisol

  1. B. A. Linquist ,
  2. P. W. Singleton,
  3. R. S. Yost and
  4. K. G. Cassman
  1. Dep. of Agronomy and Range Science, Univ. of California, Davis, CA 95616
    NifTAL Center, Dep. of Agronomy and Soil Science, Univ. of Hawaii, 1000 Holomua Rd., Paia, HI 96779
    Dep. of Agronomy and Soil Sci., Univ. of Hawaii, Honolulu, HI
    Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE

Abstract

Abstract

Despite extensive research on soil-P reactions, little is known of the effect of soil aggregation on these processes. This study was conducted to determine the role of aggregate size on the sorption and release of P in a Haiku clay (Typic Palehumult). A range of aggregate sizes up to 4 mm in diameter were used in this study. Autoradiography of sorbed 32P and P sorption studies indicated that added P was initially sorbed to a 0.188-mm layer around aggregates and remained in this peripheral layer for up to 28 d. We defined this layer as the reactive mass. Analysis of P in aggregates from a 4-yr P management field experiment on the same soil indicated that diffusion of P from this peripheral layer into the aggregate was slow, requiring >2 yr for aggregate P to reach equilibrium. When P was added to a combined mix of aggregate size fractions, P sorption increased from 55 to 245 mg P kg−1 as mean aggregate diameter decreased from 3.4 to 0.375 mm, and was linearly related to the aggregates' reactive mass (r2 = 0.96). Similarly, the reactive mass of aggregates was linearly correlated to P release from aggregates (r2 = 0.99) and to the linear buffer coefficients derived from P-sorption isotherms (r2 = 0.98). Since aggregate size is related to P sorption, soil buffering capacity, and P release from soil, it is likely that aggregation affects short- and long-term plant P availability. The effect of aggregate size, however, needs to be investigated for other soils.

Journal series number 4188 of the Hawaii Institute of Tropical Agriculture and Human Resources.

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