Municipal Sewage Sludge Use in Forests of the Pacific Northwest, U.S.A.: Growth Responses

Abstract

In nursery-bed studies, Douglas-fir, Sitka spruce, black cottonwood, and Lombardy poplar all grew well in sludge-amended media. Western hemlock and western redcedar survived poorly in aged sludge and did not appear to be good candidates for sludge applications. In most species, mixing sludge with soil provided a better growth media than sludge alone. Field studies with seedlings in cleared areas confirmed a poor survival and growth of western hemlock and western redcedar in sludge treatments. Additionally, weed competition and animal damage in cleared areas treated with sludge imposed large management costs on this option. Tree growth of cottonwoods and conifers, however, was encouraging. Applications to existing stands and plantations appears to be the most feasible management option. Growth responses in older stands were high and greater than those found for operational nitrogen fertilization in the Pacific Northwest, U.S.A. The duration of the growth response also appears to exceed those from commercial fertilizer applications.