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This article in SSSAJ

  1. Vol. 68 No. 5, p. 1645-1655
     
    Received: Dec 8, 2003
    Published: Sept, 2004


    * Corresponding author(s): astrid.oberson@ipw.agrl.ethz.ch
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doi:10.2136/sssaj2004.1645

Phosphorus Dynamics in a Highly Weathered Soil as Revealed by Isotopic Labeling Techniques

  1. E. K. Bünemanna,
  2. F. Steinebrunnerb,
  3. P. C. Smithsonc,
  4. E. Frossardb and
  5. A. Oberson *b
  1. a Univ. of Adelaide, Soil and Land Systems, Glen Osmond, SA 5064, Australia
    b Inst. of Plant Sciences, Swiss Federal Inst. of Technology Zurich (ETH), Eschikon 33, CH-8315 Lindau, Switzerland
    c Berea College, CPO 2064, Berea, KY 40404, USA

Abstract

Isotopic labeling techniques have the potential to elucidate soil P dynamics and the fate of P sources added to the soil, but they have rarely been applied to highly weathered tropical soils. We collected soils from two crop rotations [continuous maize (COM; Zea mays L.) and maize-crotalaria (MCF; Crotalaria grahamiana Wight & Arn.) fallow rotation] in a field experiment in Kenya and incubated them for 9 wk after addition of a plant residue or inorganic phosphorus (Pi), both labeled with 33P and added at 6 mg P kg−1 soil, or after carrier-free labeling of isotopically exchangeable soil phosphorus (soil IEP). The amount of P and recovery of 33P were determined in resin-extractable Pi (Presin), microbial P (Phex), and in a 0.1 M NaOH extract of samples from which Presin and Phex had been removed. The Presin increased after addition of Pi, while Phex increased after plant residue amendment, involving considerable microbial uptake of soil P. The recovery of 33P in Presin followed the order added Pi > soil IEP > plant residue, and decreased steadily from 7 to 22% after 1 d to 3 to 5% after 9 wk. The recovery of 33P in Phex remained constant throughout the incubation, being greater after plant residue amendment (15%) than in the other two treatments (4–7%). An additional 66 to 76% of 33P was recovered in the NaOH extract, as much as 27% of which was in organic phosphorus (Po) after plant residue amendment and 2 to 8% in the other two treatments. Similar to P dynamics after plant residue amendment, the comparison of the two rotations indicated a shift toward Phex and Po with increasing microbial activity due to previous fallow biomass incorporation.

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