Effects of nitrogen and boron fertilization on foliar boron nutrition and growth in two different lodgepole pine ecosystems

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Abstract
The 9-year effects of nitrogen (N) and boron (B) fertilization on the growth and foliar B nutrition of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) were evaluated in two different ecosystems in the interior of British Columbia. When added alone, B had no effect on basal area or height increment. However, combined applications of N and B were superior to N alone in stimulating height development at both study sites. At one site, fertilization with N, alone and in combination with sulphur (S), resulted in a significant amount of top dieback symptomatic of severe B deficiency. No visible deficiency symptoms were observed when B was combined with N or N + S. Boron fertilization significantly increased foliar B concentrations at both study sites, and higher foliar B levels were maintained throughout the 9-year study period. Results suggest that significant visible symptoms of B deficiency in lodgepole pine are unlikely to occur at foliar levels >6 mg/kg, although subacute B deficiency may suppress height development in the absence of deficiency symptoms. When combined with nitrogenous fertilizers, B applications of 1.5–3.0 kg/ha are likely sufficient to achieve, and maintain, favourable B status and healthy growth of trees over a prolonged period.