The longevity of Norway spruce responses to boron fertilisation

Effects of boron (B) and nitrogen (N) fertilisation on Norway spruce (Picea abies) were studied. The general hypothesis was that N further exacerbates the leader dieback induced by B deficiency whilst B corrects it. After 13 years needle B concentration was 8.4 μg g−1 in fertilised trees and 2.6 μg g−1 in controls. About half of the trees had growth disorders (leader dieback) before the fertilisation. The occurrence and severity of this was significantly reduced in B fertilised trees, yet the fertilised trees had some leader dieback. Therefore, B deficiency should be verified by needle B analysis. Boron did not affect condensed tannins; B deficiency − induced tannin accumulation does not appear to be a cause for the growth disorder. The dry mass of spruce fine roots was lowered by N fertilisation, possibly because of an increase in soil pH by the urea fertiliser and therefore locally low B availability. Boron eliminated the negative effect of N on fine roots. Boron clearly increased height growth and the effect was not declining by the end of the 13-year study period. The increase in growth did not lead to dilution effect on other nutrients, but magnesium and copper concentrations were increased by B.