Forms of phosphorus in the separates of three Tanzanian soils belonging to mollisol, alfisol and oxisol orders

Abstract

The .organic constituted the largest proportion of total P in the separates of the soils belonging to the orders Mollisol, AlfisoI and Oxisol in Tanzania. The sand fraction contained the largest amount of organic P in the Mollisol but it contained only half as much as in the clay and silt separates of the .other two soils. The proportion of .organic P to total P was higher Ln the sand of the well-drained Alfisol and Oxisol than in that off the poorly drained Molisol soil. Among the three soils, the Oxisol soil contained the lowest amounts of total inorganic P. The highest content of total inorganic P was associated with the sand fraction in the Molisol, clay in the Alfisol, and silt in the Oxisol soils. The M•P, and Fe-P were dominant in the clay and silt, and the Ca-p was dominant in the sand fraction. Virtually no reluctant soluble Fe-P Wo3JS found in the well-drained Alfisol and Oxisol soils but it constituted the second largest fraction; the first being Fe-P, in the poorly drained Molisol soil in which the content in the separates followed the order: sand Silt = clay. The contents of occluded AI-Fe-P were greater in the separates of the Molisol soil than in those of the others.