ISSN: 0041-3216 (Online), 0041-3216 (Print)
Volume 54 Number 2
Forms and distribution of phosphorus in three Nigerian soil profiles along a toposequence
The distribution of various form of phosphorus was studied in three soil profiles along a toposequence. Total phosphorus was fairly high in some of the horizons varying between 250 and 600 p.p.m. In two of the profiles, Jago and Iregun the values generally decreased with depth, but in the Iwo profile they tended to increase with depth. Organic phosphorus was generally low, decreasing with depth and reflecting the level and variation of organic carbon. In the Jago and Iregun profiles the C/P ratio were less than 200 indicating the possibility of mineralization but in the Iwo profile the ratios at the lower horizons were above 200. The relative abundance of the different active forms showed that the primary Ca-P was the most significant active P form in the poorly drained Jago profile while the secondary forms, AI-P and Fe-P, were more important in the better drained, more weathered profiles of Iwo and Iregun. In all the profiles the residual P was the most abundant form, and was regarded as P in included apatite and P occluded in sesquioxides present in the soils.