ABSTRACT
According to the Swedish government in 2006, the growth of the Swedish forest should increase 20% the following ten years, by means of fertilization, in order to replace the use of fossil fuels [1]. A similar conclusion was made during the evaluation of the Forest Bill 2007 [2]. In addition, the usage of such fertilizers in forest land should increase. The most essential nutrient for growth is nitrogen, and forest fertilization with nitrogen based fertilizers has been done over a long period [3]. An increase in growth, in the range of 15-20 m3·ha−1, is possible with a nitrogen dose of 150 kg·ha−1. Today, approximately 60,000 ha is fertilized in Sweden each year. On withdrawal of whole trees and rejected tops and branches, a larger nutrient loss is expected via needles, in comparison to the traditional collection of timber and pulpwood. In addition, the losses in growth due to nitrogen
deficiency may also follow thinning [4]. Today, wood ash is recommended in order to compensate for the nutrient output following collection of tops and branches [5]. However, the ash lacks nitrogen and may cause growth reductions in less fertile soils [6].
