Nutrient Cycling in Agroecosystems

, Volume 52, Issue 1, pp 61–65

Plant availability of phosphorus in the neutral ammonium citrate fraction of Brazilian acidulated phosphates


  • L.I. Prochnow
    • Escola Superior de Agricultura “Luiz de Queiroz”, Soil Science Department, C.P. 9, 13São Paulo University
  • J.C. Kiehl
    • Escola Superior de Agricultura “Luiz de Queiroz”, Soil Science Department, C.P. 9, 13São Paulo University
  • B. van Raij
    • Instituto Agronômico de Campinas

DOI: 10.1023/A:1016335612914

Cite this article as:
Prochnow, L., Kiehl, J. & van Raij, B. Nutrient Cycling in Agroecosystems (1998) 52: 61. doi:10.1023/A:1016335612914


In Brazil, where the rock phosphates are high in impurities, no attempthas been made to evaluate the P supplying efficiency of the neutral ammoniumcitrate fraction (NAC) of P fertilizers, or to verify if the NAC +H2O extraction solution (AOAC) is satisfactory for estimatingthe P availability. To attain these objectives, a greenhouse experiment wascarried out with samples of a Typic Hapludox soil. Four acidulatedphosphates obtained from Brazilian raw materials were studied; monocalciumphosphate p.a.[Ca(H2PO4)2·H2O]was included as a standard source of P, as well as leached samplescontaining no water-soluble P. The fertilizers were thoroughly mixed withthe whole soil in the pots or with only 1% of its volume, at the rateof 50 mg kg-1 of P, soluble in NAC + H2O. Cornplants (Zea mays, L.) were grown for 35 days and the amounts of dry matterand P accumulated in plant tops were determined. Increasing the amount ofcationic impurities in the raw materials decreased the concentration ofwater-soluble P, NAC + H2O-soluble P and water-soluble P/NAC+H2O soluble P ratio of the fertilizers obtained. The P in theNAC fraction was not as much available to plants as in the NAC +H2O fraction or in pure MCP. The great variation found in drymatter (5.4 to 17.1 g pot-1) and in P uptake (6.3 to 22.2 mgpot-1) indicates that the AOAC method is not an adequate indexfor evaluating the P availability of fertilizers with high amounts ofcationic impurities.

acidulated phosphatesavailable Pcationic impuritiescornphosphorus sourceswater soluble PZea mays
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© Kluwer Academic Publishers 1998