Effects of Demand-driven Fertilization on Nutrient Use, Root:Plant Ratio and Field Performance of Betula pendula and Picea abies

Abstract

Norway spruce [Picea abies (L.) Karst.] and silver birch (Betula pendula Roth) seedlings were grown for one season under three different fertilization regimens in the forest nursery. During the first 50 days the seedlings were grown in a glasshouse, and thereafter outdoors until the beginning of September. Finally, the plants were exposed to 16 h nights in the glasshouse throughout September. When the seedlings were supplied with fertilizers at a rate adjusted to expected plant demand (RO), less than half as much of each nutrient was applied as in a conventional regimen (RC), in which equal amounts were supplied per unit time during the growth season, yet the plants still looked healthy. Utilization of N increased by almost 50% in spruce when supply was adjusted to plant demand. In the third treatment (RL), nutrients were supplied as in the RO treatment, but at a growth-limiting rate. These plants were loaded with nutrients at the end of the season and had higher root:plant ratios, i.e. root weight in relation to total plant weight, compared with the other treatments. The nutrient status of the plants was not growth limiting at the end of the growing season in any of the treatments. The plants given the different treatments differed in size at planting out, but they had similar heights after 3 yrs in the field. This indicates that the root:plant ratio may be important for growth performance, provided that nutrient status is not at a growth-limiting level. This study suggests that the use of fertilizers can be considerably reduced in Swedish forest nurseries.