Studies of phosphate fixation and release on the bauxite soils of Jamaica I-The fate of added phosphate

E.A. Hubbard, D. Walmsley


The fate of added phosphate on two bauxite soils was studied. A fractionation technique was used to determine the forms in which added P was fixed and to trace the changes in the various forms with time. On both soils added P was fixed initially as saloid-P Al-P and Fe-P; very little was fixed as Ca-P. Over an eight week period the saloid, aluminium and calcium fractions decreased while that or the iron faction increased. The availability or added P, as extracted by Olsen's and Truog's reagents was also studied. On St Ann clay loam the percentage or added P extracted by Olsen's and Truog's reagents 72h after the addition of fertilizer P increased with increasing rate or applied P; Olsen values were about twice as high as Truog value . On Chudleigh clay loam about half of the added P was extracted by both Olsen’s and Truog's reagents at all rates of application. A decrease in available P as measured by both methods was observed over the eight week period of the experiment indicating that saloid-P and Al-P were the main sources of available P on both soils. It is suggested that because of the rapid decrease in available P after addition of phosphate to St Ann clay loam, fertilizer· phosphate should be applied close to the roots of the crop and given in split dressings on that soil.

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