Short-term boron deficiency in a black spruce (Picea mariana [Mill.] BSP) plantation

Boron deficiency was suspected as the immediate cause of abnormal needle lo ss which occurred in black spruce (Picea mariana [Mill.] B.S.P.) plantation s of northwestern New Brunswick during successive years of below normal pre cipitation. An experiment was subsequently conducted in a 21-year-old plant ation, involving foliar application of B, singly or in combination with a b roadcast N treatment. Current-year control foliage exhibited about 6 mg B k g(-1) at the end of the first growing season which was marked by below-norm al precipitation. Foliar B application, after emergence of the new foliage, raised the concentration to about 24 mg kg(-1) and resulted in a significa ntly increased mean needle mass. The needle growth response diminished as t he B concentration rose in control trees to about 10 mg kg(-1) with increas ing growing season precipitation, and no B effect on radial growth was dete cted. Addition of N resulted in both significant needle mass and basal area growth responses, but there were no B-N interactions. It is suggested that the plantation suffered a mild B deficiency at the beginning of the experi ment, that the deficiency was relieved as the mean foliar B concentration r ose above 8 mg kg(-1) with increasing growing season precipitation, and tha t moderate and severe levels of deficiency, accompanied by excessive needle loss, would have developed had the moisture deficit lasted through more th an I year and the foliage concentration of B dropped below 5 mg kg(-1). (C) 2001 Elsevier Science B.V. All rights reserved.