ABSTRACT

 Phosphorus forms (available P, total P. Organic P, active inorganic P and Inactive inorganic phosphorus) and sorption capacity were evaluated on soils modified by termites and earthworms and non-modified soils in selected areas of southeastern Nigeria. Phosphorus sorption capacity of the soil was evaluated by equilibrating 3g of soil in 30m1 of 0.OlM CaCl2containing different levels of phosphorus, 0, 2, 4, 8, 16, and 24ppm at room temperature. The Standard Phosphorus Requirement (SPR) was determined at 0.2ppm phosphorus equilibrium concentration from the sorption isotherms. Data obtained was fitted into Langmuir and Freundlich models, Maximum adsorption capacity, affinity coefficient and maximum buffering capacity (MBC) of the soils were evaluated from the models. Results obtained indicated that total P in the soils ranged from 296 mgkg 1to 882 mgkg 1with a mean value of 623 mgkg. Organic P varied from 23.70 mgkg' to 155.60 mgkg' with a mean value of 75.30 mgkg' in which the cubitermes mound and earthworm casts contained higher values than the surrounding soils and the macrotermes mound. The relative abundance of the active inorganic P fractions were in the order Fe-P > Al-P> Ca-P in both modified and non modified soils. Available P extracted by both Bray-P-I and Bray-P-2 methods correlated significantly with Al-P (r = Ø 73** , 0.79**), organic P (r = 0.77**, 0.85**) and organic matter(r = 0.68**, 0.72**).The high significant correlation of available P with Al-P. organic P and organic matter indicated that they contributed more to soil available phosphorus. The adsorption isotherms indicated that SPR ranged from 2.07 to 8.1 mgkg4. Maximum adsorption capacity ranged from 225.80 to 267.5Omgk 1and 20.14 to 71.42 mgkg 1for the Langmuir and Freundlich models respectively. High MBC was observed in all the soils with values varying from 7062.00 to 19560 m1g' in the Langmuir model. The adsorption energy obtained ranged between 26.40 to 75.00 mgkg-' in Langmuir model, and 0.2 to 0.75 mgkg in Freundlich model. A significant correlation exist between the P adsorption capacity of the soil and the clay content of the soil (r = 0.348**, 0.483*) in both models. The maximum adsorption capacity of the Langmuir model correlated negatively and significantly with organic P and organic matter present in the soils (r = - 0.319*, - 0.485*).From the study, the P sorption data of the soils fitted better with the Freundlich model with R2values greater than 0.90 than with the Langmuir model