Pedological Differences in A Cambisol in The Lower Volta Floodplain of Ghana

ABSTRACT

This study evaluated pedological differences in three soil profiles of the Amo series following cessation of seasonal flooding due to the construction of the Volta Dam. Three Pedons were used in this study. Pedon 1 is a modal profile; Pedon 2 is sited about 500m downslope from an oyster shell deposit site while Pedon 3 is on the oyster shell site. Soil properties determined include particle size distribution, hydraulic conductivity, pH, organic carbon, available and total phosphorus, exchangeable bases and acidity and dithionite extractable iron (free iron). The texture of the diagnostic horizons of pedon 1 is clayey which is typical of the Amo series. This changes to sandy clay loam in Pedons 2 and 3. Pedon 2 is underlain by sand at 110 cm depth. The increase in sand content of Pedon 2 with depth is likely due to the high contents of sandsized oyster shells.The coarse texture has influenced the greater hydraulic conductivity in the two latter Pedons. The pH of Pedon 1 is strongly acid while that of Pedon 3 is near neutral to slightly alkaline as a result of neutralization by the Ca and Mg-rich oyster shells. The CEC of Pedon 3 is higher than that of Pedons 1 and 2; the CEC of the diagnostic horizons of Pedon 3 is greater than 25 cmol(+)/kg with very low exchangeable acidity because of the influence of oyster shells. Organic carbon content in Pedon 3 is also higher because of greater biomass build up from intense biological activity. Total phosphorus concentration ranges from 122-244 mg/kg in Pedon 1, 53-173 mg/kg in Pedon 2 and 380-1444 mg/kg in Pedon 3 with corresponding available P contents of 3-9 mg/kg, 3-8 mg/kg and 6-84 mg/kg. It is apparent that phosphorus in Pedons 1 and 2 is Fe-bound because of the relatively higher concentration of free iron in these two profiles. The high P concentration in Pedon 3 is consistent with the high P content of the shells and suggest that the nutrient element is Ca-bound. Pedons 1 and 2 could be classified as Vertic Cambisol (Vertic Dytsropept) whereas Pedon 3 could be classified as Calcaric Cambisol (Vertic Ustropept). The oyster shells have modified the properties of Pedon 3 and provide a greater potential for sustainable low-input soil productivity which confirms field observations of better crop performance on this soil.