Tannery sludge compost amendment rates on soil microbial biomass of two different soils

► The high annual production of industrial wastes, such as tannery sludge, has created a series of economical, social and environmental problems. ► Soil microbial biomass and activity are early and sensitive indicators of soil stress caused by wastes. ► Composting has long been recognized as one of the most cost-effective and environmentally sounds alternatives for organic waste recycling. ► Application of tannery sludge compost in several rates may present different response of soil microbial biomass and activity in different soils.