Relationship between spacing and nitrogen fertilization of seedlings in the nursery, seedling size, and outplanting performance

Abstract

Nursery sowings of coastal and interior varieties of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), Sitka spruce (Piceasitchensis (Bong) Carr), and lodgepole pine (Pinuscontorta Dougl.) were thinned to different spacings 5 weeks after germination. Spacings in the drills, which were 15 cm apart, were 1, 2, 4, 8, and 12 cm, with the nursery sowing rate (about 0.6-cm spacing) as control. Spacings were applied factorially with three levels of N fertilizer: 60, 140, and 235 kg N ha−1. Two-year-old seedlings were planted out at Campbell River (coastal Douglas-fir) and Port Alice (Sitka spruce), both on Vancouver Island, and at Lyne Creek (interior Douglas-fir) in the Cariboo region and at Fulton Lake (lodgepole pine) in the Prince Rupert region of British Columbia. Wider spacing and greater N supply increased 2-0 seedling dry weight, root-collar diameter, and shoot height and also affected distribution of dry matter between needles, stems, and roots. Wider spacing increased survival of outplanted interior Douglas-fir by 12%. Survival of coastal Douglas-fir and Sitka spruce species was high and only increased 4 to 7% due to wide spacing after one season, but after three seasons wide spacing increased survival 17 – 19%. Compared with control, 12-cm spacing increased first-season shoot growth 53% for coastal Douglas-fir, 82% for interior Douglas-fir, and 71% for Sitka spruce. Second-season shoot growth of lodgepole pine was increased 92% by the widest spacing. Much of the improved growth was explained in terms of increased seedling size. At the highest level of N supply, increasing spacing to 4 cm did not greatly reduce yield of seedlings with root-collar diameters greater than 3 mm, except for interior Douglas-fir. Thus moderate increase in spacing improved quality without materially reducing yield of seedlings per unit area of nursery. Nursery fertilization at 235 kg N ha−1 increased new-shoot growth one season after planting by 36–58% compared with the 60 kg N ha−1 level. After three seasons the effect of higher N supply was reduced to 0–42%. High N level increased survival of coastal Douglas-fir and Sitka spruce slightly, but decreased survival of interior Douglas-fir.