Response of thinned, immature lodgepole pine to nitrogen and boron fertilization

Abstract

A study was undertaken to investigate the effects of nitrogen and boron, applied singly and in combination, on the growth of young, thinned lodgepole pine in the interior of British Columbia. Results indicate that subacute boron deficiencies without visible growth disturbance symptoms, may reduce the nitrogen fertilization response potential of lodgepole pine. Combined nitrogen and boron application significantly improved the 3-year mean height and volume increment over that obtained with nitrogen alone. Relatively small boron additions (i.e., 1.5 and 3.0 kg boron•ha−1) to the soil surface elevated foliar boron concentrations and maintained them throughout the 3-year study period. No toxic effects of boron application on foliage were observed. Both 1st-year fascicle weight response and 2nd-year branch elongation proved to be reliable indicators of subsequent stem volume response. The slightly larger stem growth response obtained with a complete fertilizer treatment, when combined with needle weight and foliar analysis data, indicates that nitrogen and nitrogen plus boron treatments may have induced a marginal sulphur deficiency. Because boron deficiency symptoms can develop rapidly following an interruption in boron uptake, and because top dieback can have such an adverse effect on stem quality and value, it is recommended that boron be added to nitrogenous fertilizer when undertaking aerial fertilization projects in lodgepole pine forests where average foliar boron concentrations are below 15 ppm.