Paper mill waste mixed with compost and other ingredients as container nursery substrates

Growth performance of container-grown dogwood (Cornus alba L. 'Sibirica'), forsythia (Forsythia x intermedia Zab 'Lynwood'), ninebark (Physocarpus opulifolius L.), and weigela (Weigela florida (Bunge) A. DC. 'Variegata Nana') were evaluated in 20 waste-derived substrates classified into five groups. Each group had 0, 20, 40 or 60% (by volume) of paper mill biosolids in binary mixtures with bark (PB group), tertiary mixtures with topsoil and sand (PTS group), and quaternary mixtures with bark, topsoil and sand (PBTS group). There were also similar binary and quaternary mixtures with compost instead of bark (PC and PCTS groups, respectively). With few exceptions, top dry weights of all four species increased (linear or curvilinear responses) with increasing rate of biosolids, and were higher in the compost-amended PC and PCTS (forsythia, 72-99 g/plant, range over all rates of biosolids; ninebark, 97-116; dogwood, 45-60; and weigela, 18-25) than in bark-amended PB and PBTS (forsythia, 26-71; ninebark, 32-80; dogwood, 33-56; and weigela, 7.7-18) substrates. Top dry weights in a control nursery mix (80:15:5 by vol bark:peat:topsoil) used by nurseries were: forsythia, 70; ninebark, 110; dogwood, 51; and weigela, 48. While none of the weigela plants attained size comparable to that of the control, top dry weights of other species reached or exceeded their control counterparts in PC and PCTS substrates over most or all rates of biosolids (all species); in PB and PBTS with 40-60% of biosolids (forsythia and dogwood); and in PTS with the highest rate of biosolids(forsythia, 91; and ninebark, 140). Higher retention of nutrients in the substrates and/or more favorable bulk densities and air-filled porosities, primarily due to the biosolids, contributed to increased growth and /or foliar nutrient status of the plants.