Abstract

A laboratory experiment was conducted to determine the effects of an initial sludge amendment on C and, primarily, N mineralization of a second sludge amendment. In this study, a municipal sludge containing Cr-tanning effluent, and a domestic sludge with little metal contamination were added to a sandy loam soil at rates of 6.65 g domestic sludge kg⁻¹ soil and 9.75 g municipal sludge kg⁻¹ soil. Sludges were reapplied 40 d later at the same rates in all sequence combinations. Respiration and nitrification were increased in sludge-amended soil. At least 70% of the total C mineralized from both sludges was evolved within the first 11 d. Initial sludge application had little effect on C evolution from subsequent applications. Nitrogen mineralized from sludge-amended soils during the initial 40 d of incubation was linearly related to time. A second application of sludge did not change the linear nature of N mineralization in all but one treatment. Ammonium N rapidly decreased and was negligible 2 weeks after sludge addition. Nitrite nitrogen levels were negligible throughout the experiment. By the end of the incubation period, the quantity of nitrate produced in all sequences of sludge addition was similar. Results indicate little effect of initial sludge addition on C and N mineralization of a second sludge amendment, even if the initial sludge applied contained a high concentration of Cr.

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