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This article in SSSAJ

  1. Vol. 57 No. 3, p. 756-760
    Received: Dec 31, 1991

    * Corresponding author(s):
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Availability of Phosphate Applied to Calcareous Soils of West Asia and North Africa

  1. E. Afif,
  2. A. Matar and
  3. J. Torrent 
  1. ICARDA, P.O. Box 5466, Aleppo, Syria
    Departamento de Ciencias y Recursos Agrícolas y Forestales, Universidad de Córdoba, Apdo. 3048, 14080 Cordoba, Spain



The relative influence of different soil components on P availability in calcareous soils is contradictory in the literature. For this reason, P-incubation experiments were conducted on 19 soils from different agricultural areas of West Asia-North Africa. The soils contrasted widely in clay, CaCO3, and Fe oxide contents. The availability index (AI), the ratio between the increase in Olsen P and the P applied, was determined between 30 and 240 d after applying rates between 20 and 500 mg P kg−1 soil. The Al at 20 mg P kg−1 (AI20) changed little with time after 60 d. The AI20 at 180 d was negatively correlated to the Fe oxide content and to the cation-exchange capacity of the soils. In a stepwise regression procedure, the variance of AI20 that was accounted for increased significantly from 44 to 56, and then to 70% by including Fe oxides, cation-exchange capacity, and CaCO3 content. At a rate of 500 mg kg−1, AI500 decreased more markedly with time and was negatively correlated, at all times, with the amount of CaCO3 but not correlated with Fe oxides, cation-exchange capacity, or clay content; at some times, a positive correlation was found between AI500 and organic matter. These results (i) support the idea that P reactions in calcareous soils differ according to the P application rate, and (ii) raise caution about the incubation conditions in the laboratory that are used to estimate the loss of P availability in calcareous soils.

Joint contribution from ICARDA (International Center for Agrícultural Research in the Dry Areas) and the Departmento de Ciencias y Recursos Agrícolas y Forestales, Universidad de Córdoba.

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