Raw and Composted Paper Mill Sludges and Municipal Compost in Nursery Substrates

Abstract

Silverleaf dogwood (Cornus alba L. `Argenteo-marginata'), forsythia (Forsythia × intermedia Zab. `Lynwood Gold'), and weigela (Weigela florida Bunge A.DC. `Red Prince') were grown in #2 (6-L) containers filled with 100% bark or bark mixed with 20%, 40%, or 60% (by vol.) each of raw paper mill sludge (RB group), composted paper mill sludge (CB group), a proprietory paper mill sludge-derived compost (PB group), and municipal compost (MB group). A fifth substrate group (MH) consisted of 100% hemp chips or hemp chips mixed with the same rates of municipal compost. The containers were trickle-irrigated and fertilized with a controlled-release fertilizer. Among the bark-amended groups, growth was highest for dogwood and forsythia with PB, increasing dramatically and peaking at ca. 40% rate (68 and 94 g/plant top dry weight, respectively). Growth of these species was intermediate with MB and CB and least with RB, increasing to rates ≥ 50% in these groups, except for a nonsignificant response of dogwood to RB. Growth of weigela increased equally with PB and MB substrates up to ca. 40% (117 g/plant), but was unresponsive to rates of RB and CB. With the hemp-amended MH group, growth of all three species increased to rates ≥ 50% (62, 93, and 116 g/plant for dogwood, forsythia, and weigela, respectively). Growth of the three species over most rates of all substrate groups was similar to, or exceeded, that in 80% bark: 15% peat: 5% topsoil, a proven nursery mix. Top dry weight of all three species was positively correlated with soluble salts concentrations in the substrates at planting after first irrigation (0.23-1.72 dS·m-1, range over all substrates) and at various intervals during the season.