Growth and foliar nutrition of western red cedar fertilized with sewage sludge, pulp sludge, fish silage, and wood ash on northern Vancouver Island

Abstract

The fertilizer efficacy of a variety of organic wastes was tested in a 9-year-old plantation of western red cedar (Thujaplicata Donn ex D. Don) growing on a cutover of cedar–hemlock (Tsugaheterophylla (Raf.) Sarg.) forest on northern Vancouver Island. Seven treatments were compared: municipal sewage sludge, sewage sludge plus pulp sludge, fish silage and wood ash, silage and ash plus pulp sludge, wood ash alone, ammonium nitrate with triple super phosphate, and control (untreated). Each treatment was replicated three times. Rates of application were 225 kg N•ha−1 in the inorganic fertilizer and about 500 kg N•ha−1 in the organic wastes (except wood ash). The height and diameter of the cedar trees 2 years after fertilization were greatest in the plots treated with inorganic fertilizer (average height was 274 cm, vs. 211 cm in control plots; average diameter at 30 cm was 49 mm, vs. 34 mm in control plots). Smaller but significant growth responses were achieved with sewage sludge and fish silage plus ash. Mixtures of sewage sludge or silage with pulp sludge produced smaller height growth responses, but did not affect diameter growth. Wood ash alone had no effect on tree growth. All treatments except wood ash increased the concentrations of macronutrients in foliage. Foliar N concentrations were greatest in trees treated with fish silage or inorganic fertilizer. Stagnated plantations of western red cedar appear to provide an opportunity for recycling these organic wastes.