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

Abstract

The forms and distribution of phosphorus in selected soils formed over different parent materials in Abia State of Nigeria were investigated. Total P varied widely ranging from 175.6 to 1252.45 mg / kg with overall mean of 450.68 mg/ kg. Ajata soils having higher values while Amakama have lower values. The organic P also varied widely ranging from 31.03 to 127.71 mg /kg with a mean value of 61.0 and 92.91 mg/ kg respectively. About 40% of the Total P in the surface horizon (Ap) of the fine-textured soils (Ajata ) are in organic P form while the coarse-textured soils ( Amakama ) 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 comprise 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. There is high content of Al-P in the lower horizons of the Ajata soil. Available P is low with values ranging from 4-21 mg/ kg with a mean value of 11.59 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.