Finnish Forest Research Institute  Metla

Media Release 10.10.2005

Boron fertilization in Norway spruce stands cures growth disturbances

Boron deficiency causes different levels of growth disturbance in forests. Especially in eastern Finland attention has been paid to growth disturbances associated with spruce stands on fertile mineral soils. Boron fertilization can be used to help affected trees to recover. After fertilization, boron concentration in needles increased significantly even during the first growing season. Boron fertilization increases height growth of trees but does not have a clear effect on diameter growth.

Boron deficiency seems to retard height growth before any disorder symptoms become apparent, since healthy trees also benefit from boron fertilization. However, nitrogen fertilization alone seems to have a detrimental effect on height increase of severely damaged trees. This information is presented in the recently published paper by Metla researchers Anna Saarsalmi and Pekka Tamminen.

The experiments were performed in three approximately thirty-year-old Norway spruce (Picea abies) regeneration stands of Oxalis-Myrtillus type (OMT) in the Kuopio, Tuusniemi and Kaavi regions. Healthy, slightly damaged and severely damaged trees were selected as sample trees. The trees were individually fertilized in May 2000 with boron (B), boron and phosphorus (B+P), or nitrogen (N). The control trees were not fertilized. Soil and needle samples were collected from the experimental stands. The sample trees were measured before fertilization and again in September 2003, i.e. four growing seasons after fertilization. Recovery of the sample trees was estimated at the same time.

Four growing seasons after fertilization a high proportion of the disturbed spruces had recovered irrespective of the fertilizer treatment . However, B fertilization significantly improved the recovery of the trees. There were hardly any severely damaged trees among the trees fertilized with boron. Compared with B alone, the application of P together with B gave no additional benefit. Prophylactic measures seem to be the best way to handle a B deficiency problem, i.e. to prevent growth disorders with B fertilization in advance.

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