Soil fertility and spontaneous revegetation in lignite spoil banks under different amendments

In order to study the reclamation of mine sites, the short-term effects of different amendments on soil fertility (at 1 and 6 months) and spontaneous vegetation (at 3 and 6 months) were examined in spoil banks of a lignite mine in Galicia (NW Spain). Experimental plots were established on three spoil banks deposited in 1984, 1988 and 2007, and treated with compost, limestone, NPK or no amendment (control trials). Fertilizer type, time after application and bank age, and their mutual interactions, were found to have significant, early effects on soil quality and fertility in terms of pH, CECe, the organic matter, total nitrogen, and exchange cations contents, as well as on vegetation establishment, composition, and species richness and diversity. The effects of each type of amendment, its ability to correct limitations to plant production and its influence on the successful establishment of spontaneous pioneer species are discussed. Compost gradually corrected P limitations (from 4 to 37 mg kg−1, in the oldest spoil bank) and significantly improved plant production with respect to untreated spoils (from 1905.1 to 4165.3 kg ha−1 DM). Unlike NPK, compost contributed towards maintaining species diversity and richness. It was found to significantly boost metabolic activity in the edaphic flora, which was estimated from the soil respiration rate as determined by infrared gas analysis (IRGA). Limestone facilitated the establishment of legumes and other dicotyledons, and corrected pH (from 5.3 to 7.0) and Al saturation in CEC (from 37.62% to 0.20%) in the most recent spoils, but produced imbalances in exchange cations (Ca/Mg = 25.7) due to excessive Ca supply. Based on our results, using compost in recent lignite spoils requires the gradual correction of soil pH with magnesium limestone to avoid Mg limitations.