Nutrient status of vegetation grown in alkaline bauxite processing residue amended with gypsum and thermally dried sewage sludge - A two year field study

Although the treatments for overcoming the high pH and exchangeable sodium percentage (ESP) of bauxite residue are well known, there is little information on long-term nutrient management of vegetation after rehabilitation. The present study examined the chemical and physical amendment of fine fraction residue (red mud) at the Aughinish Alumina Ltd. Bayer Plant, Ireland followed by a two-year field investigation. Gypsum and sewage sludge were incorporated into the residue and amended mud sown with Lolium perenne and Holcus lanatus. Aerial portions were harvested and nutrient composition determined annually for the first two years growth. Amended substrate was low in manganese and magnesium. After year one herbage contained adequate calcium levels, but there were deficiencies for nitrogen, manganese, potassium and magnesium. Sodium levels were not considered excessive and levels declined further in year two. Levels for nitrogen, calcium, manganese, magnesium, phosphorous and potassium were also reduced in the second year. As levels were already deficient in year one the further decreases suggest severe nutrient shortage in the residue substrate. For long-term success of revegetation of bauxite residue, even after gypsum and organic amendment, the deficiencies of nutrients in the substrate must be overcome.