Mining disturbance alters phosphorus fractions in northern Australian soils

The brown kandosol soils at Weipa, North Queensland, contain little soil phosphorus (P). Plant-available fractions (considered in this study to include resin, hydroxide, and dilute acid extractable P) approximate 85 μg P/g, or 70% of total soil P, the majority of which is in labile organic forms, highlighting the importance of P cycling within the native eucalypt forest. A field experiment was undertaken to evaluate the effect of soil handling during bauxite mining on the distribution of P between the various soil fractions. This study showed that soil stripping and replacement disrupts the P cycle and affects the proportional distribution of P between soil fractions. Horizon mixing during soil handling severely reduces the size of plant-available soil P fractions in surface soils ( 0-5 cm depth) and this can only be partially compensated by the addition of fertiliser. A survey of rehabilitated sites of differing ages showed that restoration of soil organic P fractions is extremely slow, with the overall distribution of P within replaced soils remaining different from that within undisturbed soils 15 years after rehabilitation to native forest or exotic pasture species.