The Impact of the Quality of Coal Mine Stockpile Soils on Sustainable Vegetation Growth and Productivity

Stockpiled soils are excavated from the ground during mining activities, and piled on the surface of the soil for rehabilitation purposes. These soils are often characterized by low organic matter (SOM) content, low fertility, and poor physical, chemical, and biological properties, limiting their capability for sustainable vegetation growth. The aim of the study was to evaluate the impact of stockpile soils of differing depth and quality on vegetation growth and productivity. Soils were collected at three different depths (surface, mid, and deep) as well as mixed (equal proportion of surface, mid and deep) from two stockpiles (named Stockpile 1: aged 10 and Stockpile 2: 20 years) at the coal mine near Witbank in the Mpumalanga province of South Africa. Soils were amended with different organic and inorganic fertilizer. A 2 × 4 × 5 factorial experiment in a completely randomized blocked design with four replications was established under greenhouse conditions. A grass species ( Digiteria eriantha ) was planted in the pots with unamended and amended soils under greenhouse conditions at 26–28 °C during the day and 16.5–18.5 °C at night. Mean values of plant height, plant cover, total fresh biomass (roots, stems and leaves), and total dry biomass were found to be higher in Stockpile 1 than in Stockpile 2 soils. Plants grown on soils with no amendments had lower mean values for major plant parameters studied. Soil amended with poultry manure and lime was found to have higher growth rate compared with soils with other soil amendments. Mixed soils had better vegetation growth than soil from other depths. Stockpiled soils in the study area cannot support vegetation growth without being amended, as evidenced by low grass growth and productivity in this study.