Abstract
Because the agricultural use of tannery sludge may cause increased risks to soils, composting is recognized as one of the most suitable alternative for tannery sludge recycling. Experiments were conducted under field conditions to evaluate the effects of composted tannery sludge (CTS) on the soil microbial biomass and trace elements after two years of consecutive applications. The following five treatments were used: 0 (without CTS application), 5, 10, 20 and 40 ton ha -1 of CTS (dry basis). Soil samples were collected at 60 days after the CTS application at 0-20 cm depth. The CTS application promoted changes in the soil microbial biomass C (SMB-C) and N (SMB-N). In the first year, significant increases in the SMB-C and SMB-N were observed with the application of 10 ton ha -1 . Furthermore, CTS application increased the Cr content in the soil after two years of application.
Highlights
The tannery industry occupies an important place in the Brazilian economy with assets of 21 billion dollars per year (SILVA et al, 2010)
Because the composted tannery sludge (CTS) was found to be rich in organic matter, its application increased the soil organic C (SOC) content in both years (Figure 1)
The increase in the SOC content after the application of CTS is a direct response to the high organic matter content in the waste, as reported by Gupta and Sinha (2007) who found an increase in the SOC after the application of tannery sludge to soils in India
Summary
The tannery industry occupies an important place in the Brazilian economy with assets of 21 billion dollars per year (SILVA et al, 2010). This industry releases 1 million tons of tannery sludge annually, of which 3% is solid waste (SANTOS et al, 2011). There are no established methods for tannery sludge disposal in Brazil, and landfilling is commonly used. The application to soil has been suggested as a suitable method (SINGH; AGRAWAL, 2008). Both methods have a series of associated economic, social and environmental problems. It is necessary to develop news methods for tannery sludge recycling as an alternative to landfilling and soil application
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