Abstract
Effective application of organic residues to reclaim soils requires the optimization of the waste management to minimize CO2 emissions and optimize soil C sequestration efficiency. In this study, the short-term effects of pig slurry amendment alone and together with marble waste on organic matter mineralization in two tailing ponds from Cartagena-La Unión Mining District (SE Spain) were investigated in a field remediation experiment. The treatments were: marble waste (MW), pig slurry (PS), marble waste + pig slurry (MW+PS), and control. Soil carbon mineralization was determined using a static chamber method with alkali absorption during 70 days. Soil respiration rates in all plots were higher the first days of the experiment owing to higher soil moisture and higher mean air temperature. MW plots followed the same pattern than control plots, with similar respiration rates. The addition of pig slurry caused a significant increase in the respiration rates, although in MW+PS plots, respiration rates were lower than in PS plots. The cumulative quantities of C-CO2 evolved from the pig slurry mineralization were fitted to a first-order kinetic model explaining 90% of the data. This model implies the presence of only one mineralisable pool (C0). The values of the index C0*constant rate/added C were similar for PS plots in both tailing ponds, but lower in the MW+PS treatment, suggesting that the application of marble reduces the degradability of the organic compounds present in the pig slurry. Thus, the application of marble wastes contributes to slow down the loss of organic matter by mineralization.

Keywords: Carbon mineralization, tailing pond, heavy metal, marble waste, pig slurry

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