Soil solution chemistry of two reclamation sites in the Lusatian lignite mining district as influenced by organic matter application

Due to a large reclamation (recultivation) demand in the Lusatian lignite mining district, efficient strategies for the rehabilitation of abandoned mine sites are needed. A field study was conducted for comparing the effects of three different fertilizer treatments (mineral fertilizer, sewage sludge and compost) on soil solution chemistry of both a lignite and pyrite containing spoil as well as a lignite and pyrite free spoil. The lignite and pyrite containing spoil was ameliorated with fly ash from a lignite power plant (17-21 t ha(-1) CaO), whereas the lignite and pyrite free site received 7.5 t ha(-1) CaO in form of limestone. Fertilizer application rates were: mineral fertilizer 120 N, 100 P and 80 K kg ha(-1). 19 t ha(-1) sewage sludge and 22 t ha(-1) compost were applied. Soil solution was sampled in 20, 60 and 130 cm depth for the period of 16 months. Solution was collected every fortnight and analysed for pH, EC, Ca2+, Mg2+, K+, Na+, Fen+, Aln+, Mn2+, Zn2+, NO3-, NH4+, SO42-, Cl-, PO43-, C-inorg and DOC. Lignite and pyrite containing spoil differed clearly from lignite and pyrite free spoil regarding soil solution concentrations and composition. Acidity (H+) produced by pyrite oxidation led to an enhanced weathering of minerals and, therefore, to at least 10 fold higher soil solution concentrations compared to the lignite and pyrite free site. Major ions in solution of the lignite and pyrite containing site were Ca2+, Mg2+, Fen+, Aln+ and SO42-, whereas soil solution at the lignite and pyrite free site was dominated by Ca2+, Mg2+ and SO42-. At both sites application of mineral fertilizer led to an immediate but short term (about 1 month) increase of NO3-, NH4+ and K+ concentrations in soil solution down to a depth of 130 cm. Application of sewage sludge caused a long term (about 16 months) increase of NO3- in the topsoil, whereas NO3- concentrations in the subsoil were significantly lower compared to the mineral fertilizer plot. Compost application resulted in a strong long-term increase of K+ in soil solution, whereas NO3- concentrations did not increase. Concentrations of PO43- in soil solution depend on solution pH and were not correlated with any treatment.