Amelioration of the physical properties of slate processing fines using grape marc compost and vermicompost
The effect of grape marc compost and grape marc vermicompost on the soil physical characteristics of slate processing fines, a waste produced during the processing of slate blocks, has been evaluated in two short-term studies. In the first study, the slate processing fines were mixed with the composts at three rates (4, 8, and 16% dry weight, equivalent to approximately 60, 120, and 240 Mg ha–1), and incubated in the laboratory for 90 d at 25°C. The increment of organic matter, available organic C and biological activity were used to explain the effect of the treatments on the soil physical properties. The compost amendment significantly increased the consistency, water holding capacity, and aggregate size and stability of the slate processing fines (P < 0.05). Water holding capacity and consistency were positively correlated to total organic C, whereas aggregate stability was correlated to hot water-extractable C and dehydrogenase activity. The second study was a field experiment to evaluate the effect of a grape marc vermicompost on the hydraulic properties of the slate processing fines. The fines were mixed with two rates of grape marc vermicompost (4 and 8%, equivalent to approximately 60 and 120 Mg ha–1). The moisture retention characteristic curve of the slate processing fines shifted to higher values of moisture at both rates of the amendment, but the hydraulic conductivity was only increased at the highest rate. The results of both experiments suggest that the addition of organic amendments can significantly improve the physical properties of mining wastes, producing a soil-like material which could be of use in restoration.