Nursery growth of conifer seedlings using fertilizers of different solubilities and application time, and their forest growth

Abstract

Douglas-fir (Pseudotsugamenziesii (Mirb.) (Franco) and white spruce (Piceaglauca) (Moench) Voss) seedlings were grown in a bare-root nursery for two growing seasons with one of four fertilizers, Osmocote (17-7-12) (OSM), ammonium phosphate (11-55-0) (AMP), ammonium sulphate (21-0-0) (AMS), or Hi-Sol (20-20-20) (HIS), each supplying one of three levels of N: 0, 210, or 350 kg N ha−1, at two different frequencies throughout the growing seasons. Fertilizers, levels, and frequencies were arranged in a factorial design and replicated in three blocks on each species. Additionally, Douglas-fir seedlings that had been grown for two seasons without fertilization were treated with the same amounts, as supplied over two seasons, of AMP, AMS, and HIS between 1 September and 20 October, as a late-season treatment. After two seasons, mean dry weight differences due to fertilizers were, for Douglas-fir seedlings: AMP > AMS > HIS = OSM, and for white spruce seedlings: AMS = AMP > HIS > OSM. Dry weight was increased by increasing level of fertilizer. Fertilization increased shoot growth compared with root growth and resulted in seedlings having more dry matter in stems and less in needles at the end of two seasons. Dry weight of 2-0 white spruce was correlated with soil pH (r2 = 0.61) NO3 (r2 = 0.57), and P (r2 = 0.34) measured in September of the first growing season, indicating that fertilizers affected growth by their influence on these factors. Measurements made at planting showed late-season fertilized Douglas-fir had higher N and P tissue concentrations than growing-season fertilized trees. On average late-season fertilized trees had 6% higher survival than growing-season fertilized trees after planting in the forest. Survival appeared related to needle N concentration at planting, with maximum survival occurring at about 2.1% N. Height and stem volume relative growth rates were higher for late-season fertilized trees, although growing-season fertilized trees were still 9% taller than late-season fertilized trees after three seasons in the forest. Results suggested that fertilizer solubility was not as important for nursery growth as fertilizer composition, and its effect on soil pH, and that late-season fertilized stock might outperform growing-season fertilized stock in the forest.