Är bor nödvändigt vid skogsgödsling i Sverige?

Abstract: This thesis has been made on behalf of SCA Skog AB to assess the need of boron in Swedishforest fertilization. Boron has been added to Swedish forest fertilizers since the beginning of the1980s. This makes the fertilizers more expensive and therefore has the necessity of boron inSwedish forest fertilization been raised.The Swedish bedrock generally contains small amounts of boron. The boron in the bedrock istightly bound to the mineral tourmaline and mostly unavailable for plants. This leads to that thecontribution of boron to the soil from weathering is very low besides soils with marinesediments. Boron added to the soil originates by most parts from atmospheric deposition andweathering of organic matter. The deposition levels differ in different parts of Sweden. Innorthern Sweden the deposition levels are low except from a belt along the coastline. The levelsin southern Sweden are considerably higher. Therefore most of the boron supply to the trees hasto be covered by weathering of organic matter, especially in northern Sweden.The boron levels in the majority of the surveys found in literature have been lowered afterfertilization. Despite the lower levels of boron, growth disturbance have in most cases onlyoccurred to a limited extent. When growth disturbance have occurred the stand has beenfertilized more than one time and with shorter interval than practiced in commercial forestry. Thestands were with few exceptions located in the inland of northern Sweden. The amount ofnitrogen applied to the stands exceeded in most cases the levels 150 kg/ha, which are normallyapplied in commercial forestry. The lack of growth disturbance indicates that the boron suppliedby deposition and above all from weathering of organic matter was sufficient to cover the boronneeds of the trees, even though the trees have been fertilized previously. Growth disturbanceafter a first fertilization are nonexistent in Sweden. If growth disturbance occur after the secondor third fertilization, the economical effect will be limited due to that the damage will occur at atree height where the quality is of less importance.With the amounts and interval that are used in commercial forestry today, the risk of substantialgrowth disturbance is low in growing stand. The knowledge on how the following treegenerationis affected by previous fertilization without boron is not sufficiently examined. The risk of borondamages in young stands is concidered to be minimal since young forests have lower demands ofboron and that surveys of the boron needle level show that the boron levels in needeles returnclose to the original level when the fertilizition effect has declined.To exclude boron in forest fertilization involves risks of negative economical effects, but theresult of the littearture studie indicate that this risk are considered to be low in most stands wherefertilization will be conducted.