Individual study: The use of organic waste and inorganic fertilizer addition to improve revegetation of iron ore-mine tailings at Norberg, Västmanland, Sweden
Borgegard S. & Rydin H. (1989) Utilization of waste products and inorganic fertilizer in the restoration of iron-mine tailings. Journal of Applied Ecology, 26, 1083-1088
Iron ore mining in the vicinity of the village of Norberg in the Bergslagen region of Sweden, has produced a waste product of sandy-loamy texture which is deposited in tailings. Dust from these tailings causes problems for people in the vicinity and it has become highly desirable to establish a vegetation cover to resolve this problem. Nitrogen and phosphorus deficiency is considered an important constraint on vegetation establishment on iron mine wastes and water holding capacity and temperature regimes are also generally unfavourable.
The use of sewage sludge, horse dung, NPK-fertilizer, and NPK-fertilizer plus bark was tested in an attempt to improve yields of grasses and clover sown on these iron-mine tailings.
Study area: The study was undertaken on a 15 ha area of abandoned mine tailings close to the village of Norberg (c.100 m away from a built up area), Västmanland central Sweden. The tailings were sparsely vegetated with aspen Populus tremula, grey alder Alnus incana, willows Salix spp, downy birch Betula pubescens, silver birch B.pendula, timothy Phleum pratense, red fescue Festuca rubra, reed Phragmites australis and rosebay willow-herb Chamerion (Epilobium) angustifolium. The tailings consisted of 6% clay, 30% silt, 50% fine sand and 14% coarse sand. In nearby tailings, (deposited at the same time as the one studied), the total content of heavy metals was: 17,000 ppm Fe, 13 ppm Zn, 64 ppm Cu and <0.6 ppm Cd.
Experimental design: In September 1984, plots of 5 x 5 m in three randomized blocks with 4-m wide pathways in between, were treated with sewage sludge, horse dung, and bark plus 300 or 600 kg/ha of NPK fertilizer, or were untreated. Organic matter treatments were applied once (a 10-cm layer); with sewage sludge and bark, the material was either mixed with the tailings or deposited on the surface; horse dung was mixed in to be effective. The horse dung was composted for 1 year and the bark for at least 8 years.
The plots were sown in late May 1985 with 100 kg/ha of a seed mix containing 37.5% F.rubra, 12.5% common bent Agrostis (capillaris) tenuis, 12.5% smooth meadow grass Poa pratensis, 12.5% perennial rye-grass Lolium perenne, 12.5% Festuca trachyphylla and 12.5% white clover Trifolium repens and fertilized (except for plots with sewage sludge or horse dung) with 20:5:9 NPK fertilizer. The area was fenced to prevent trampling and grazing.
Sampling and soil analysis: Samples of the above-ground green biomass was harvested in September 1986. The sown and invading species were sorted, dried at 105°C and weighed. Soil samples for determining water-holding capacity were taken in June 1987 and in September 1988 for pH, phosphorus and nitrogen.
Plant growth: At the end of the second growing season, the sludge-treated plots had a very dense, 60 cm tall, sward with F.rubra contributing up to 90% of the total dry mass of the sown species, and up to 50% in horse dung, NPK fertilizer and the control plots. Its proportional yield was less bark-treated plots where T.repens grew well and comprised 34-48% of the dry mass of sown species. A.tenuis, P.pratensis and L.perenne combined never exceeded 40% of dry mass. According to total dry matter of the sown species, the treatments could be arranged as: sewage sludge (3180-3940 g/m²) >horse dung (1930 g/m²) >bark (570-750 g/m²) >NPK fertilizer (50-140 g/m²) >control (30 g/m²). When bark was added with the fertilizer, the level of fertilizer (300 or 600 kg/ha) had no effect.
Nutrient content: Phosphate content decreased with depth in all treatments, but no consistent trend was detected for nitrate or ammonium.
Water-holding capacity: Addition of organic matter led to a slight increase in water-holding capacity: mean values were 51% for sludge, 56% for horse dung, 58% for bark, 40% for fertilized plots without bark and 43% for control plots
Conclusions: Addition of only fertilizer had little effect. With addition of fertilizer and bark, a grass sward was successfully established, and with sewage sludge and horse dung the cover was very dense. The water-holding capacity was improved by the addition of the organic material.
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