Long term effect of municipal waste disposal on soil properties and productivity of sites used for urban agriculture in Abakaliki, Nigeria.

An assessment on the impact of long term (20 years) municipal waste disposal on soil physicochemical properties and soil productivity in municipal waste dump sites was carried out in urban Abakaliki, southeastern Nigeria. Profile pits were dug at selected points and auger and core samples were collected from different soil horizons of dump and non-dump sites using free survey technique to choose observation points. There were differences in particle size distribution between dump and non-dump sites. Similarly, soil bulk density was lower by 9-13% while total porosity and hydraulic conductivity were higher by 9-14% and 240-463%, respectively, in the dump site relative to non-dump sites. Soil organic matter, total nitrogen, cation exchange capacity (CEC) and percent base saturation increased from 701 to 743, 646 to 740, 7% to 10% and 5% to 14%, respectively, in the dump site soil relative to non-dump site soil. These results were confirmed by a high coefficient of alienation (degree of unrelatedness, square root(1 - R2)) in bulk density, 0.65; total porosity, 0.58; hydraulic conductivity, 0.87; organic matter, 0.93; total N, 0.82; pH, 0.85 and cation exchange capacity, 0.97 between dump and non-dump soils. Heavy metals (Pb, Cu, Fe and Zn) increased by between 214% and 2040% in dump site soils relative to non-dump site soil. This may lead to increased uptake of metals by some test crops although their transfer ratios differ from crop to crop. Long term dumping of municipal wastes can influence soil properties and productivity at municipal waste dump sites but still may be used for farming provided that ecotoxological risks associated with its usage are continuously assessed and controlled.