Growth of pedunculate oak (Quercus robur L.) seedlings on blendsubstrates based on consolidated brackish sludge

Abstract

Either in its pure form or as a base for a blend-substrate, brackish sludge can be used as a growth medium for trees. The objectives of the experiment were (1) to evaluate the quality of consolidated brackish sludge as a growth medium, (2) to assess the influence of substrate blending on tree growth (leaf area, tree height, biomass), and (3) to evaluate the need for substrate blending. Germinated acorns of the same mother tree were planted in containers and grown under controlled conditions. The substrate consisted of pure brackish sludge or of brackish sludge blended with peat, sand or wood chips, in stages of 25 volume percentage. Chemical analysis of the brackish sludge showed a neutral pH, a conductivity of 3.60 mS/cm and a sufficient amount of macro elements. The addition of sand contributed to an accelerated desalination of the substrate. The treatments with 100 % sludge and 25 % peat yielded a leaf area, a tree height and a biomass which were among the top three growing results. The growing results of the treatments with 25% sand and 50% peat were consistently among the top five. The blending of peat in brackish sludge had no influence on leaf area, tree height and biomass of seedlings. The use of wood chips or of more than 25 % sand resulted in a significant decrease of these three growth parameters. Foliage analyses of the trees grown on a substrate containing more than 50% sand or wood chips revealed deficits in available nutrients. These deficits manifested themselves in a loss of leaf area, tree height and biomass production. The nutritional status and the growth parameters of oak seedlings on brackish sludge were favourable. No influence of the salt and the heavy metal concentrations on growth was observed. Consolidated brackish sludge is a suitable growth medium for trees.