Use of paper mill sludge for the acclimation of nursery trees planted in urban soil

Trees planted in urban areas often suffer in the phase of transplanting. Transplanting is always a shock for plants, especially when they are moved from the nursery, where the environmental conditions are very favourable, to urbanized areas, where resources and maintenance are scarce. Moreover, some properties of urban soils, such as alkaline pH and compaction, make it difficult for trees to adapt. The industry of recycled paper produces tons of waste, which is a clean material composed mainly of cellulose that potentially can be used as a component in plant growing media. In the present experiment, the pelletized de-inking paper mill sludge has been added to the substrate with the aim of increasing the water storage and, at the same time, of contrasting compaction. Three species, Quercus ilex, Lagerstroemia indica, Prunus serrulata 'Kanzan', were planted in 40-L pots using two substrates: i) control, composed of peat+pumice (75%), green waste compost (20%) and zeolites (chabasite) 5%; ii) experimental, composed of municipal green waste compost (MGWC) 61%, pellet of de-inking paper mill sludge (PDS) 20%, pumice 13% and zeolites (chabasite) 6%. The substrates were analysed for pH, organic carbon, total nitrogen, electrical conductivity and cation exchange capacity, and plants' responses were monitored by measuring trunk diameter, shoot length and chlorophyll content (SPAD). The experimental substrate resulted suitable to grow the trees in nursery. To use the waste in the experiment, we undertook a path to get permission from the local authorities who manage the industrial waste.