Mixtures of paper mill sludge, wood chips, bark, and peat in substrates for pot-in-pot shade tree production

Abstract

There is little scientific information on substrates for pot-in-pot shade tree production. The objective of this research was to examine various organic-waste-derived substrates for growing shade trees in pot-in-pot systems. Seedling whips of green ash (Fraxinus pennsylvanica Marsh.), Japanese birch [Betula platyphylla var. japonica (Miq.) Hara], and silver maple (Acer saccharinum L.) were grown for two seasons in 76-L containers. The containers were trickle irrigated and fertilized with controlled-release fertilizers. Treatments included a control nursery mix (50% by volume of pine bark:15% compost:35% topsoil) and nine other mixes classified into three groups: Group I (25, 50 or 75% bark mixed with 50, 25, or 0% wood chips, and 25% paper mill sludge); Group II (25, 50 or 75% bark; 50, 25 or 0% wood chips; and 25% peat); and Group III (25, 50 or 75% peat; 50, 25 or 0% wood chips; and 25% paper mill sludge). In both years, trunk diameters of the three species were greatest with Group III substrates, intermediate with Group II, and least with Group I. Trunk growth was positively correlated with water retention porosity, which ranged from 42 to 57%, 38 to 42%, and 20 to 27% for Groups III, II, and I, respectively. Trunk diameters of Group II and III trees were equal to, or slightly exceeded (10–12%), those of the nursery mix. The nursery mix had a water retention porosity of 49% and generally the highest content of soluble salts. The high-peat (50 and 75%) substrates marginally but consistently produced trees with the largest trunk diameters, although with birch (not the other species) shorter trees resulted as the peat content increased. Key words: In-ground containers, nursery, ornamentals, waste utilization, container culture