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This article in SSSAJ

  1. Vol. 61 No. 3, p. 752-764
     
    Received: Mar 25, 1996


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doi:10.2136/sssaj1997.03615995006100030008x

Inorganic Phosphorus Transformation and Transport in Soils: Mathematical Modeling in ecosys

  1. R. F. Grant  and
  2. D. J. Heaney
  1. Dep. of Renewable Resources, Univ. of Alberta, Edmonton, Alberta, Canada T6G 2E3
    Plant Industry Division, Alberta Agriculture, Edmonton, Alberta, Canada T6H 4P2

Abstract

Abstract

The movement and uptake of P in soils occur primarily in the soluble phase, so that the reliable simulation of P movement and uptake requires that the concentrations of soluble P forms be explicitly represented in mathematical models. To represent soluble P concentrations under dynamic boundary conditions, a convective-dispersive model of P transport has been coupled to a model of P transformation in which adsorption-desorption, precipitation-dissolution, and ion pairing are explicitly represented as concurrent equilibrium reactions. This model is used to explain the temporal and spatial distribution of P among soluble and resin-, NaHCO3-, NaOH-, and HCl-extractable fractions in soils following amendment with KH2PO4. Simulated reductions in soil pH following different P amendments caused solid-phase P in the model to be recovered more from resin- and NaOH-extractable forms and less from HCl-extractable forms as solution P concentration increased. These changes were consistent with those observed experimentally using a P fractionation procedure on a Malmo silt loam (Typic Cryoborall) following its equilibration with 0 to 512 mg L-1 of KH2PO4 and following its irrigation for 205 d with 50 mg L-1 of KH2PO4. Simulated displacement of cation coprecipitates from exchange sites allowed the model to reproduce the temporal and spatial patterns of water- and HCl-extractable P in resin columns of different cation-exchange capacities following a KH2PO4 surface amendment. The results of model testing suggest that changes in soluble P concentrations following P amendments may be represented from concurrent equilibrium reactions for adsorption-desorption, precipitation-dissolution, and ion pairing. However, the rate at which these reactions proceed remains uncertain.

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