Phosphorus status of some semi-arid agricultural soils of northern Ghana
1995
Owusu-Bennoah, E., Department of Soil Science, University of Ghana, Legan, Ghana; | Ampofo, J.G., Irrigation Development Authority, Ashaiman, Accra, Ghana | Acqua Y, D.K., Formerly of Department of Soil Science, University of Ghana, Legan, Ghana)
The phosphorus status of selected soils of the semi-arid savanna zone of northern Ghana was studied by determining their available organic and lotal P content and the P sorption characteristics. The available P varied from 1.7 to 8.7 mg kg-', total P from 116 to 215 mg kg-' and organic P from 63-125 mg kg-'. The organic P formed about 61 per cent of the total P and the C:P ratio was mainly below 150. The capacity to sorb P varied among the soils, but in general the soil developed over basic parent material (greenstone), sorbed more phosphorus than those over acidic rock (granite). The P sorption maximum values correlated significantly with organic carbon (r = 0.964*) and free iron extractable with dithionite-citrate (r 0: 0.958*) but not with pH, CEC and clay. Thus, free iron oxide and organic carbon in the soils were the main factors responsible for P sorption, accounting for 97 per cent of the observed variation. It is recommended that the use of organic residues and manur~ and application of inorganic fertilizers to supply about 30-35 kg P ha-' would improve P availability in these soils.
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