PHOSPHORUS SORPTION AND PROPERTIES OF FERRUGINOUS NODULES FROM SEMIARID SOILS FROM GHANA AND BRAZIL

The morphology of ferruginous nodules from Ghana and Brazil was examined, and their P sorption potentials and P sorption related to chemical and morphological properties of soil fines and nodules were measured. Despite already elevated P contents of nodules, sorption capacities of ferruginous nodules were higher than those of soil fines. In a residual fertilizer trial, nodules acted as an effective sink for P, removing P from plant-available pools in the soil and fixing about 180 kg P ha-1 over 3 years. Micromorphological observation showed significant porosity in nodules, and X-ray microprobe scans revealed high Fe and Al concentrations in pores and on nodule surfaces. These properties allow the penetration of nutrient solutions into inert-appearing lateritic nodules, and cause very efficient and rapid fixation of phosphate.