Effect of soil reclamation process on soil C fractions

Mine soils are notable for their low organic matter content. Soils in the depleted copper mine in Touro (Galicia, Spain) were vegetated with trees (eucalyptuses and pines) and amended with wastes (sewage sludge and paper mill residues) to increase their carbon concentration. Two different zones at the mine (settling pond and mine tailing) and their respective treated areas (vegetated and/or amended) were sampled and analysed with the aim of evaluating in depth the effect of the reclamation treatments on both the concentration and quality of soil organic matter under field conditions. The results showed that the two treatments (tree vegetation and waste amendment) significantly increased the organic C in the mine soils from 1.4-6.6 to 10-112 g kg−1. However, only the soil amended with wastes in the settling pond reached the usual values of undisturbed soils (92-126 g TOC kg−1 soil). Amending with wastes was also the only treatment that increased the soil humified organic C concentration to proper values and therefore also the microbial biomass C. We recommend the use of organic wastes for amending soils poor in organic matter as well as the regular application of this treatment, as the nitrogen supply can be more limiting for plant growth than the organic C.