Sludge utilization by trees in Hungary

Abstract

Pot and field experiments with liquid sewage-sludge, for improving poor sandy soil and its utilization by forestry, have been conducted by the Afforestation Department of the University for Forestry and Timber Industry since 1977 for VITUKI (Research Institute for Water Management). The following tree species were involved in the experiments: Italian poplar, “Robusta” poplar, white willow and black locust. Doses of sludge used were 0 (control), 500, 1000, 2000, 3000 and 4000 m 3 ha −1. There were four repetitions, treatments being multiply repeated. From this experiment the following conclusions can be drawn. Best results were attained when “I-214” poplar was fertilized with a sewage-sludge dose of 1000 m 3 ha −1. This treatment was carried out in the dormant season and repeated in a second year. The best dose for “Robusta” poplar was 500 m 3 ha −1. In the case of “I-214” poplar, doses of sludge greater than indicated above resulted in positive effects, but these were somewhat reduced by the harmful salt concentrations caused by the sludge. For “Robusta” popular, 2000 and 3000 m 3 ha −1 doses were of negative effect in comparison with the control plants. There was no justifiable positive effect of sludge treatment for other tree species. Weeds have proved to be good indicators for the degree of sludge treatment. The more sludge had been given to it the more weedy was the soil. Untreated control plots were practically weedless. There was no evidence that toxic materials and heavy metals would accumulate in the trees at higher quantities of sludge.