Phosphate Sorption Capacity, Bonding Energy and Buffering Mechanisms of Wetland Soils in Akwa Ibom State, Nigeria

Abstract

Phosphate sorption capacity, bonding energy and buffering capacity of wetland soils in Akwa Ibom State, Nigeria were assessed for effective and sustainable soil management. Three wetland types (inland depression, river floodplain and coastal swamp) were selected for the study. In each wetland type, three locations were selected (9 locations) and in each location, soil samples were collected from 3 points at the depth of 0 -30cm and bulked to form composite samples using soil auger and taken to the laboratory for analysis. In the laboratory, a solution containing 0, 20, 40 and 80 ml prepared from 6.15g of KH2 PO4 (Potassium hydrogen phosphate) in 1500ml of distilled water and make up to two (2) litres with distilled water was used for the study. 2.5g of soil samples were weighed into a 50ml plastic cup and 2.5ml of each of the 4 sorption treatments solution were added to each of the soil in the cups and mixed thoroughly for effective mixing of P solution with the soil. The set ups were covered and incubated for 7 days. The treated soil samples were watered with deionized water once to keep the sample moist throughout the period of incubation. On the 7th day, P in each of the treated soil samples and the leachate were extracted using Bray-P-1 extractant. The P in the extract was determined using Murphy and Riley method. The P extracted from the soil samples were considered to be P adsorbed while P in the leachate samples were considered to be P in solution. Langmuir equation was used to estimate P adsorption capacity, bonding energy and P buffering capacity of the soils. The results showed that floodplain soils had the highest mean phosphate adsorption capacity (0.50 mgkg -1 ), followed by soils of inland depression (0.32 mgkg -1 ) while coastal swamp soils had the least (0.09 mgkg -1 ). The trend was as follow: floodplain soils > soils of inland depression > coastal swamp soils. Coastal swamp soils had the highest bonding energy (0.54 Lmg -1 ), followed by floodplain soils (0.27 Lmg -1 ) while soils of inland depression had the least (0.07 Lmg -1 ). The trend was as follow: coastal swamp soils > floodplain soils > soils of inland depression. Floodplain soils had the highest maximum buffering capacity (0.047), followed by coastal swamp soil (0.042) while soils of inland depression had the least (0.018). The trend was as follow: Floodplain soils > coastal swamp soils > soils of inland depression. Hence, the three wetland soil types were not the same in P sorption capacity, bonding energy and buffering capacity.

Physico-chemical properties of soils derived from different geologic formations in typical rainfall agro-ecological zone

“…The porosity of the soil obtained from the different geologic formation shows the nature of the geologic formation to be sandy in nature and sandy soils are known to have high porosity rate [6]. The lowest porosity range was found in Ogwashi geologic formation which depicts a sand stone property, while Imo had the highest porosity within the different geologic formations of the study area.…”

“…The silt content of the soils sampled show that Alluvium had the highest silt content which signifies that soils from Alluvium geologic formation are basically from the activities of the river [6], while the amount of silt content sampled across other geologic formations shows low silt content. The coefficient of variance (0.20 to 1.43) of the silt content across the different depth of the geologic formation shows that the silt content are similar with depth but different with geologic formations.…”

“…The pH of the soils obtained from the different geologic formation shows that the soils are acidic in nature. The pH of the geologic formations is found to be suitable for plant growth and development [18], hence encourages crop productivity.…”

“…Therefore, soil represents a lot of meaning to different profession, based on their usage. [6] studied the influence of parent materials on mineral association and sorption capacity of soils in Akwa Ibom state, using a profile pits. [7] in their study compared the physical properties and organic matters of soils derived from three (3) different parent materials of Akwa Ibom state.…”