Effect of Late-season Top-dressings of N (and K) applied to Conifer Transplants in the Nursery on their Survival and Growth on British Forest Sites

Abstract

At two English forest nurseries, transplants of five conifer species— Picea sitchensis, Picea abies, Tsuga heterophylla, Abies grandis , and Pinus contorta —were grown with fertilizer supplying N, P, K, and Mg in amounts intended to be adequate for producing healthy green trees with nutrient concentrations in the ‘sufficiency range’ as determined by earlier experiments. ‘Luxury uptake’ of nitrogen was obtained with top-dressings of ‘Nitro-Chalk’ applied in the nursery during early September, when top growth had nearly ceased. Tests of the effect of this extra N on forest establishment were repeated in four successive years under a wide range of soil and climatic conditions, keeping the trees in a cold store during each winter and planting them on forest sites in England, Scotland, or Wales during the following spring. Except for Grand fir, nitrogen advanced bud-break of all species during the first summer after planting and had no deleterious influence on survival. It tended to increase growth of Sitka spruce during the season after planting, but in later years the differences became small in relation to tree size. The effects on other species were small, except for one considerable decrease in the growth response of Grand fir at a single site. Frost damage of Sitka spruce of Washington origin was severe on a Welsh and a Scottish site where this frost-sensitive provenance would not normally be grown. At the Welsh, but not the Scottish site, the nitrogen treatment increased the damage. In the few experiments (confined to Picea sitchensis ) which tested late-season potassium in the nursery, K concentrations were increased from deficiency to barely sufficiency level; growth in the forest was increased in two of the four experiments. The extra K had no effect on frost damage.