SORPTION OF PHOSPHORUS IN SOILS IN THE SEMI DECIDUOUS FOREST ZONE OF GHANA

The study conducted investigated phosphorus (P) sorption at varying depths of the soil column and the results were interpreted with reference to some physico-chemical properties of the soils. The samples were taken from soil depth of 0-30 cm from two land use systems (a cocoa plantation and an arable land under the cultivation of cowpea). The soil samples were packed into a transparent polyvinyl chloride (PVC) cylinders and the phosphorus solutions applied at 69 ppm. After, 72 hours, the soil samples in the PVC cylinders were carefully taken and sectioned at 5 cm interval, that is, 0-5, 5-10 and 10-15 cm. Soil separates were air-dried and the P content determined. The vertical distribution of phosphorus through the soil column decreased significantly with depths in soils under both land-use systems. The soil under the arable land sorbed more P than the cocoa plantation soils at soil depths of 0-5 and 5-10 cm. The contrary occurred at the soil depth of 10-15 cm where more P was sorbed by soil under the cocoa plantation. The study showed that soil organic matter content, hydraulic conductivity and water flux density could hinder the sorption capacity of soils. Also, the impact of aluminium and iron to fix phosphorus in acidic soils is hindered by the above soil properties. The differences observed in the P sorption capacities of the soils suggested that, the use of blanket phosphate fertilizer recommendations may not be a good strategy as it may lead to under application or over application of P in some areas with the consequence of compromising crop yields or freshwater quality.