Soil biology of low grade landfill soil with sewage sludge amendment

The aim of the present study was to evaluate the feasibility of using sewage sludge for ameliorating landfill cover soils by assessing soil biology and nutrient cycling because of the poor physical property and nutrient contents. An acidic sandy loam of these low graded subsoil materials commonly used for landfill cover. soil was amended with sewage sludge at 0, 2.5, 5, 15 and 35% w/w fresh weight. An increase in the sludge amendment rate caused a rise in both pH and electrical conductivity (EC). However, with incubation time, pH decreased while EC increased and then declined. Nevertheless, salinity and heavy metal contents of the sludge amended soil were all within the toxic limits. Soluble NH4+-N, NO3--N and PO43--P increased after amending the soil with sewage sludge. However, increasing the sludge application rate decreased the N mineralization efficiency and created an adverse effect on nitrification, while the P- mineralization efficiency was enhanced by sludge amendment. The sharp peaks of NH4+-N at day 21 with a concentration of 280 and 520 mg kg(-1) for 15% and 35% sludge amended soil would probably be a limitation to plant growth. Soil respiration, as an indicator of microbial activity, demonstrated the same pattern for all treatments that CO2 evolution increased initially and then decreased until the end of incubation. The peak soil respiration was at day 7 for all treatments, except for the soil amended with 35% of sludge which had a peak at day 2 and of much higher lever than others. The present results indicated that a sludge amendment rate of 5 to 15% would have the optimal beneficial effects on the cover soil quality in terms of microbial activity and nutrient mineralization.