Phosphorus Forms and Distribution in Selected Soils Formed Over Different Parent Materials in Cross River State of Nigeria

Abstract

The forms and distribution of phosphorus in selected soils formed over different parent materials in Cross River State of Nigeria were investigated. The parent materials of the soils are Cretaceous Sandstone, Olivine Basalt, and Crystalline Basement Complex Rock in Ogoja, Otiri Ikom and Atimaka Yala Ikom respectively. The result of various forms of phosphorus indicated that the pattern of their distribution with depth was not uniform in all the soils studied. Total P varied widely ranging from 181.7 to 693.9 mg / kg with overall mean of 337.46 mg/ kg. Ikom Red soils having higher values while Ogoja have lower values. The organic P also varied widely ranging from 62.86 to 136.49 mg /kg with a mean value of 75.61 mg/ kg. About 40% of the Total P in the surface horizon (Ap) of the fine-textured soils (Ikom Red) are in organic P form while the coarse-textured soils (Ogoja and Ikom grey soils) have a very low (< 20%) organic P contribution to total P. The inorganic fractions of the soils occurred in the sequence of occluded P> Fe-P> Al-P> Ca-P. The occluded P constitutes between 26 and 68% of the total P in the various soils and 40 to 80% of the total inorganic P. The occluded P and Fe-P comprised more than 84% of the total inorganic P. The content of Ca-P and Al-P were very low (<16% of the total inorganic P). The active inorganic P constitutes between 18 and 38% of the total P. Available P is low with values ranging from 5-22 mg/ kg with a mean value of 13.72 mg /kg. The surface horizon (Ap) contains more available P than the subsurface soil horizons. The multiple correlation analysis revealed that total P correlated negatively with sand and positively with clay, exchangeable Ca, occluded P, organic P, Ca-P, Fe-P. Organic P correlated positively with Fe-P, Al-P and Total P. Ca-P correlated negatively with sand and positively with organic carbon, exchangeable Ca, Al-P and Total P. Fe-P correlated positively with organic P, Al-P and total P. Al-P correlated positively with Fe-P, Ca-P and organic P. The occluded P correlated positively with clay and exchangeable Ca and negatively with sand and pH.