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In this work, the efficacy of two different strategies, used for 20 years (1992–2012) to restore a lignite mine dump, was investigated. The reclamation strategies were selection of the sterile materials, avoiding surface placement of pyritic materials, or surface application of topsoil material. Representative plots corresponding to each of both strategies were selected, as well as a control plot where reclamation techniques were not applied. An increase in total C, soluble Al, and exchangeable Al, as well as a decrease in pH, electrical conductivity, sulfate, and exchangeable cations concentrations took place during the study period. Avoiding pyritic materials on surface was the strategy giving the best acid–base conditions in the whole period, showing higher pH values (6.1–6.7) than application of topsoil (4.7–5.3), as well as the highest exchangeable Ca values (0.71–6.83 vs. 0.55–3.00 cmol(+) kg−1), and less exchange Al (0.22–2.80 vs. 0.99–3.72 cmol(+) kg−1) and soluble Al (0.04–0.60 vs. 0.19–37.47 mg L−1). Regarding fractionation of Al in soil solution, labile forms predominated throughout the study period, although organic forms (nonlabile Al and acid‐soluble Al) showed an increase over time, which was in accordance with an increase in C concentration. The most toxic Al species (Al3+ and Al‐OH) were less abundant where pyritic materials were not placed on surface, compared with plots treated with topsoil (which did not differ from control plot for most parameters). The results of the study indicate that surface application of topsoil would not be justified as strategy to effectively restore lignite mine dump areas. [ABSTRACT FROM AUTHOR]

Andisols are characterised by having abundant reactive Al in the form of short-range ordered (SRO) Al constituents and organo-Al complexes, which facilitates the accumulation of soil organic matter (OM). However, recent studies of New Zealand pastoral systems have reported loss of carbon (C) from Andisols when under intense management. This study compares the organic and inorganic chemistry of Andisols on two adjacent pasture sites under different pastoral management regimes (Paddock 2 being more intensively managed than Paddock 1), as well as under a nearby pine stand (Forest). Mean soil pH-H2O in Forest (5.3) was significantly lower (P < 0.05) than that in Paddock 1 (5.7), which itself was significantly lower (P < 0.05) than in Paddock 2 (6.1). Soil C concentrations were significantly higher (P < 0.05) in the soils under pasture than under pine (63.8 g C/kg), and C in Paddock 1 (98.1 g C/kg) was significantly higher (P < 0.05) than in Paddock 2 (84.1 g C/kg). The ratio of Al in organo-Al complexes (as estimated with sodium pyrophosphate) to the sum of Al in both SRO and organo-Al complexes (Alp/Alo) was significantly smaller (P < 0.05) as the alkalinity of the soils increased (0.38, 0.23, 0.16 for Forest, Paddock 1 and Paddock 2, respectively). At the molecular level, soils under Forest had a larger relative contribution of degraded products of plant polysaccharides than those under pasture, while these had a larger contribution of fresh (e.g. cellulose and cutan/suberan aliphatic structures) and N-rich OM (e.g., microbial fingerprints, denoting a high microbial activity). Dissolved organic C content in the rhizosphere of pasture species was similar between paddocks, but Paddock 2 had a significantly (P < 0.05) greater contribution of organic acids of MW < 500 Da and higher pH (6.8 vs. 6.2). The results (1) confirm the common enrichment in organic C of New Zealand top soils under pasture compared to those under pine, and (2) reveal that the changes in the soil chemistry associated with pasture management may weaken the ability of these soils to preserve OM. [ABSTRACT FROM AUTHOR]