Nitrogen mineralization in soils treated with tannery sludge

Abstract

The objective of this work was to evaluate nitrogen mineralization in two tannery sludges in soils. A Rhodic Acrustox and a Typic Haplustox received four levels of each sludge (0, 595, 1,190 and 1,785 kg ha^-1 N): a liming sludge (LCL), comprising very low chromium contents and a primary sludge (LCR), with 17 g kg^-1 Cr. Soil-sludge mixture was placed in percolation tubes and periodically leached after incubation up to 132 days. First order kinetic model described the nitrogen net mineralization (R² = 0.967** to 0.998**). Compared to LCL, the addition of LCR caused a decrease in the percentages of the accumulated mineralized nitrogen from sludges (averages 35.5 and 4.0%, respectively), a decrease in the mineralization rates constants (averages 0.028 and 0.0048 day^-1) and substantially increased the T_1/2 (ranging from 267 to 100 and from 29 to 19 days), indicating N mineralization inhibition, possible due to the high chromium content of that sludge. A detailed analysis of mineralization curves with LCR applications pointed that there are three phases that probably represent successive adaptations of the microbiota to different recalcitrant fractions.