Applying different doses of tannin coagulated dairy sludge in soil: Influences on selected pollutants leaching and chemical agronomic attributes

The aim of this study was to evaluate the impact of soil amendment with tannin coagulated dairy industry sludge on fertility chemical attributes and on the release of selected pollutants. To do so, we conducted soil column leaching and soil incubation experiments, with different doses of such residue. Sludge was obtained through thermal dryer or bed drying processes. The results showed that the application of the studied residues did not cause improvement in the release of evaluated pollutants (phenol, NO3− and Cl−). However, for chemical attributes, like pH, value raised from 4.5 in the blank probe to 8.7 and 7.2 in the maximum doses of thermal and bed dried sludge respectively. Based on pH raising, critical doses for application of studied sludges were tested: 11.3 t.ha-1for thermal processed and 64.6 t.ha-1for bed dried sludge. At the critical doses, for thermally dried sludge, we observed improvements in effective cation exchange capacity (ECEC), from 3.61 cmolc. dm-3 (in the blank probe) to 6.57 cmolc. dm-3, cation exchange capacity (CEC) at pH 7.0, from 6.65 cmolc. dm-3 to 7.85 cmolc. dm-3, decreasing in potential acidity, from 4.23 cmol.dm-3 to 1.41 cmol.dm-3and exchangeable aluminium was not detected since the lowest applied dose. For the bed dried sludge, at critical doses, ECEC and CEC were improved to 6.64 cmolc. dm-3 and 7.69 cmolc. dm-3 respectively. The potential acidity in the critical dose was 1.45 cmol.dm-3,and exchangeable aluminium was decreased from 0.95 cmol.dm-3(in the blank probe) to 0.12 cmol.dm-3. Bases saturation and organic matter (OM) content were also increased. The effects over all the studied parameters, except OM, were more perceptible for thermally dried sludge due to lime addition in the drying process. We concluded that the application of the studied residues in agriculture is a feasible option.