Responses of six species of Proteaceae, in containers, to controlled-release fertilizer

Seedlings of Adenanthos sericeus, Banksia ericifolia, Banksia hookeriana, Conospermum caeruleum, Protea cv. Masquerade, and Leucadendron cv. Sundance were grown in a soilless potting medium containing controlled-release Osmocoteo fertilizer (17:1.6:8.7) at eight treatment levels: 0, 1.25, 2.5, 3.75, 5.0, 6.25, 12.5, and 3 18.75 kg m(-3). After 6 months, shoot dry mass and the concentrations of nitrogen (N), phosphorus (P), and potassium (K) in recently matured leaves were determined. At the lowest rate of applied fertilizer, growth was stunted for all species. Maximum shoot dry mass was associated with a fertilizer rate of 2.0 kg m(-3) for L cv. Sundance, 2.5 kg m(-3) for C. caeruleum and B. ericifolia, and 3.75 kg m(-3) for P. cv. Masquerade, B. hookeriana, and A. sericeus. At the highest fertilizer rate, for all species except A. sericeus, plants displayed foliar symptoms typical of fertilizer excess, and growth was reduced. A range of concentrations of N, P, and K in leaves at optimum growth was determined for each species.