Natural plant colonization improves the physical condition of bauxite residue over time.

Freshly stacked bauxite residue in Central China has little vegetative growth probably as a result of its poor physical condition and chemical properties which deter plant establishment. Over the last 20 years, spontaneous plant colonization on the deposits has revealed that natural weathering processes may improve bauxite residue to the extent that it can support vegetation. Bauxite residue samples were collected from a chronosequence and analyzed to determine the effect of natural processes over time. The freshly stacked residue showed considerable physical degradation, having a high bulk density, low porosity, and poor aggregate stability. Through natural processes over a 20-year period, the texture changed from a silty loam to a sandy loam, porosity was enhanced (43.88 to 58.24 %), while improvements in both aggregate stability (43.32 to 93.20 %) and structural stability (1.33 to 5.46 %) of the stacked residue were observed. Plant growth had a positive effect on pH, exchangeable sodium percentage, soil organic carbon, water-stable aggregation, and structural stability, probably due to the presence of plant roots and associated microbial activity. It was concluded that natural processes of regeneration, stabilization, and attenuation have improved the hostile physical environment of bauxite residue allowing plant establishment to take place.