Rehabilitating open-cut coal mine spoil for a pasture system in south east Queensland, Australia: Abiotic soil properties compared with unmined land through time

Abstract

Rehabilitation of mined land intends to support food and biomass production, with open cut mines required to return the land to a safe, stable and productive state in Queensland, Australia. The aim of this investigation was to assess the potential for soil that was previously farmed, then mined and rehabilitated to support pasture for commercial cattle production. The study was focussed on abiotic properties of the rehabilitated soils, in comparison to properties of a range of unmined soil profiles supporting pastures within the immediate vicinity. Three hypotheses were tested: 1) the abiotic properties of rehabilitated soils would fall within the range of those from nearby unmined soils; 2) that rehabilitated soils would support viable pasture production; and 3) that the mine-spoil would restrict root function. The mine was situated near Acland, Queensland, with rehabilitated land sown to pasture 1, 3 and 6 years prior to the initiation of the study in 2013. The investigation followed these rehabilitated sites, in comparison to a Control site, and 18 proximal unmined sites, through a five year period. All sites were used to support cattle grazing, with soil nutrients, structural condition and pasture growth (8 sites) monitored. Evidence from pasture production and root exploration obtained through soil pit investigations demonstrated that the mine spoil was capable of supporting root growth beyond the replaced soil layer. There were few differences between the Control and rehabilitated sites with regard to benefits or constraints to pasture production, with exception that two rehabilitated sites had simillar or higher plant-available phosphorus and nitrogen. It was concluded that: 1) abiotic properties of rehabilitated soils fell within the range of unmined soils; 2) viable pasture production was achieved from the rehabilitated sites; and 3) both the replaced soil layer and the mine spoil supported root exploration and pasture production.