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This article in SSSAJ

  1. Vol. 61 No. 5, p. 1355-1363
     
    Received: Aug 16, 1996


    * Corresponding author(s): n.menzies@mailbox.uq.oz.au
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doi:10.2136/sssaj1997.03615995006100050010x

Chemical Characterization of Soils of a Tropical Humid Forest Zone: A Methodology

  1. N. W. Menzies  and
  2. G. P. Gillman
  1. Dep. of Agriculture, Univ. of Queensland, St Lucia 4072, Australia

Abstract

Abstract

A methodology, based on a combination of routinely performed analyses and investigation of fundamental charge and anion sorption properties, was used to characterize the soils of the humid forest zone of Cameroon. In general, the soils have about 2 cmol kg−1 permanent negative charge, with about 1 cmol kg−1 from variable-charge sources at current soil pH values. Furthermore, they are improverished with respect to Ca, Mg, and K, while Al frequently dominates the exchange complex. Thus, the ability of these soils to retain base cations is more limited than is suggested by the cation-exchange capacity (CEC). Therefore we propose the concept of a degradation index (DI) defined as: DI = 100(CEC5.5 − sum of basic cations)/CEC5.5, where CEC5.5 is the CEC measured at pH 5.5. This index encompasses degradation a soil may have experienced from natural or man-made causes. Extractable PO4 concentrations are considered very low and the soils have a moderate to high capacity to fix added PO4. Surface soil SO4 concentrations are considered marginal to deficient for plant growth, though adequate reserves of SO4 are held in the subsoil by SO4 sorption. The approach used demonstrated that the five morphologically different soil profile classes identified in the zone have similar chemical characteristics. Thus, the results of experimentation conducted on one of the soil profile classes will be applicable throughout the zone. Furthermore, the approach has provided a means of identifying comparable soil types in other parts of the world and will guide technology transfer. The analytical methods used in this study are relatively simple and require no specialized equipment, and are therefore within the capabilities of many laboratories in the developing world.

Contribution from the International Institute of Tropical Agriculture, Humid Forest Station, Yaounde, Cameroon.

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