Nutrient status of pasture ecosystems established on rehabilitated overburden and topsoil sites in the Hunter Valley, New South Wales

Abstract

The rehabilitation of disturbed areas at the Howick Coal Mine (Hunter Valley, New South Wales) involves re-creating pasture ecosystems. Some sites are rehabilitated using topsoil, whereas others are established directly into the overburden mine waste due to the low availability and poor quality of topsoil. Pastures on both substrate types are then maintained by periodic applications of fertiliser. A comparison was made between nutrient levels held in the soil and the roots and stems of the dominant pasture grass (Rhodes grass, Chloris spp.) in an overburden (rehabilitated in 1990) and a topsoil site (rehabilitated in 1991). Sampling was conducted in autumn 1998 at 3 random locations along 3 replicate transects established on both substrates. Laboratory analyses were conducted to determine levels of N, P, S, Ca, K, Mg, and Na for both soil and plants samples; Mn, Fe, Zn, Cu, and Al for the plant samples only; and NO ₃-N, PO ₄-P, organic carbon, pH, and EC for the soil samples only.

Multivariate analysis showed a distinct difference in the nutrient status of topsoil and overburden sites, across the 7 nutrients common to the roots, stems, and soil. The concentration of all macronutrients was significantly higher in the overburden compared with the topsoil sites. The majority of macronutrients were in greatest concentrations in the stems but the highest levels of micronutrients were found in the roots. There was a higher concentration of micronutrients in the overburden sites. Both of the rehabilitated sites had adequate macronutrient concentrations of S, Ca, Mg, and K. However, there were deficient concentrations of NO₃-N in both the topsoil and overburden sites and a deficient concentration of PO₄-P in the topsoil site. Long-term management options to improve the nutrient status of rehabilitated coal mines in the Hunter Valley include increased grazing, increasing fertiliser inputs, and burning the rehabilitated areas.