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Soil Science Society of America Journal Abstract - Soil Chemistry

Phosphate Solubilization from Poorly Crystalline Iron and Aluminum Hydroxides by AVAIL Copolymer


This article in SSSAJ

  1. Vol. 81 No. 1, p. 20-28
    Received: Aug 01, 2016
    Accepted: Nov 05, 2016
    Published: December 29, 2016

    * Corresponding author(s): sadoydor@ncsu.edu
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  1. Sarah Doydora *a,
  2. Dean Hesterberga and
  3. Wantana Klysubunb
  1. a Dep. of Crop and Soil Sciences North Carolina State University 101 Derieux Pl. Raleigh, NC 27695
    b Synchrotron Light Research Institute P.O. Box 93 Nakhon Ratchasima Thailand 30000
Core Ideas:
  • Dissolved P increased with increasing co-additions of AVAIL and P to metal oxides.
  • AVAIL dissolved greater P with Al-hydroxide than with ferrihydrite.
  • AVAIL had no effect on P bonding distribution between Al(III) and Fe(III) in mixed sorbents.


Less than 40% of fertilizer phosphate applied to soils is generally taken up by crops because of strong retention of P by soil solids. Our objective was to determine mechanisms by which AVAIL, a maleic-itaconic copolymer used as a fertilizer additive, potentially affects retention of applied phosphate, and consequently plant availability. We measured competitive sorption of AVAIL and orthophosphate in aqueous suspensions of ferrihydrite and poorly crystalline Al hydroxide [pxl-Al(OH)3] at pH 6.2, and characterized phosphate bonding distribution between Fe(III) and Al(III) in 1:1 (w/w) mixtures of these solids using P K-edge X-ray absorption near edge structure (XANES) spectroscopy. With increasing co-additions of AVAIL and P at the levels evaluated, sorption results showed dissolved P increasing up to 0.45 and 1.25 mM for ferrihydrite and pxl-Al(OH)3, respectively, which represented 18 and 34% of added P. Negative relationships between sorbed P and sorbed AVAIL implied a competitive adsorption mechanism between these two ligands, and solubilization of Fe by AVAIL indicated complexometric dissolution of ferrihydrite. The XANES results showed that 72 to 86% of sorbed P was bonded with Al(III) in the ferrihydrite/pxl-Al(OH)3 mixtures, with only a minor (<15%) effect of AVAIL apparent when P was applied at the two levels tested in this study. Our results suggest that optimized AVAIL application rates for enhancing crop availability of P would depend on soil sorption characteristics and the soil content of residual P relative to its soil sorption capacity.

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