PHOSPHORUS IN GYPSIFEROUS SOILS - THE INFLUENCE OF SOIL PROPERTIES ON P-FRACTIONATION

This paper presents the results of a study into the status and distribution of P in six gypsiferous soil profiles collected from Iraq and southern Spain. A selective extraction procedure based on a modified version of that developed by Chang and Jackson was used. The concentrations of total P and the different inorganic P fractions declined with depth in all the soil profiles. The forms of the inorganic P fractions when expressed as a percentage of the total P decreased in the order: Ca-bound P much greater than reductant-extractable P > Al-bound P > Fe-bound P > organic P > NH4Cl-extractable P. There was little difference between profiles or horizons in this general pattern of distribution. The Ca-bound fraction ranged between 61.9 and 78.6% of the total P in different horizons. It is concluded that the behaviour of P in gypsiferous soils is dominated by its interactions with Ca supplied by gypsum.