Response of soil enzyme activities to synergistic effects of biosolids and plants in iron ore mine soils

Past mining activities in Swaziland have left a legacy of abandoned mine sites (iron ore, asbestos, diamond and coal mine dumps), all of which have not been reclaimed. These sites were recently (2013) considered by the country’s wastewater treatment authorities as suitable places where biosolids can be applied, firstly as a biosolids disposal alternative and, secondly, as a strategy to accelerate mine soil remediation through phytostabilization. In order to understand the effects that this might have on mine soil conditions and microbiota, two (2) plant growth trials were conducted in biosolid-treated ironmine soils and one (1) trial on undisturbed soil, under greenhouse conditions, for twelve (12) weeks. According to the results obtained, the combination of biosolids and plants led to significant improvements (p<0.05) in parameters related to soil fertility. Significant increases(p<0.05) in alkaline phosphatase, b-glucosidase and ureasesoil enzyme activities were also observed. Copper and zincwere significantly (p<0.05) increased (Cu from 17.00–50.13 mg kg^-1; Zn from 7.59–96.03 mg kg^-1); however, these sludge-derived metals did not affect enzyme activities. Improvements in soil physicochemical conditions, organic matter–metal complexes, effects of plants on metals and the essentiality ofCu and Zn to soil enzymeswere thought to havemasked the effects of metals. Increases in soil enzyme activities were considered to be indicative of improvements in the quality, fertility health and self-purification capacity of iron mine soils due to synergistic effects of biosolids and plants.