The maintenance of grassland on smelter wastes in the Lower Swansea Valley. 3. Zinc smelter waste.
Large-scale trials, using applications of organic materials and pulverized fuel ash on Zn smelter waste, were set up in the Lower Swansea Valley, UK, in 1965 and monitored until 1970. Growth on most of the treatments declined markedly in 1968 and 1969. Annual fertilization failed to prevent this decline, which was attributed to the recurrence of Zn toxicity. The most successful treatments in the long term were 15.0- and 22.5-cm coverings of pulverized fuel ash, followed by annual NPK fertilization. Initial application of a 5-cm layer of sewage sludge or a 7.5-cm layer of pulverized fuel ash gave satisfactory cover of pasture at first but was not satisfactory in the long term. Zn-tolerant populations were not affected in this way and showed satisfactory long-term growth on waste amended with organic materials but required annual NPK fertilization.