Assessment of sewage application in south-eastern Nigeria - Part 1: Impact on selected soil morphological and physical properties

This work investigated the impact of long-term application of sewage sludge/effluent on morphological and physical properties of a sandy Ultisol (Arenic Kandiustult) in Nsukka, Nigeria. Soil samples were collected from the surface (0-20 cm) of a sewage-amended soil and from unamended control fields, after which two representative profile pits were also sited on the sewage-amended plot and two on the control fields. Soil samples were collected at specific intervals from these pits. Morphologically, both soils were deep and well drained, with no concretions or mottles. The colour variation ranged from dark reddish to brownish black for the first layer of the profile pits in the area amended with sewage sludge, to reddish brown and red in others. In unamended soils, the colour ranged from dark reddish brown in the top layer to reddish brown and red in others. Texture was generally sandy loam over sandy clay loam in amended soil, and sandy clay loam in unamended soil. The structure was generally weakly granular in the top layer, but moderately subangular in other subsurface layers. The entire area is on a gentle slope of <5%. Soil organic matter, bulk density, total porosity and aggregate stability were enhanced significantly (p <0.05) in the sewage-amended soil compared with the non-sewage-amended soil. Changes in the saturated hydraulic conductivity, field capacity and micro- and macro-porosities were not significant. The results indicate that application of sewage sludge and effluent has little impact on the morphology of these soils. However, it had a positive impact on the physical properties of the soils. But it should be used with caution because of its known negative effects on heavy metal accumulation in soils when used at high rates and for long periods.