FOLIAR NUTRIENT STATUS AND FASCICLE WEIGHT OF LODGEPOLE PINE AFTER NITROGEN AND SULFUR FERTILIZATION IN THE INTERIOR OF BRITISH-COLUMBIA

The effects of nitrogen and nitrogen + sulphur fertilization on the first-year fascicle weight and foliar nutrient status of immature, thinned lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) were evaluated at seven locations in the interior of British Columbia. The results indicate that sulphur deficiencies, either aggravated or induced by nitrogen fertilization, may limit the responsiveness of lodgepole pine to nitrogen additions. At four locations, combined sulphur and nitrogen additions improved the sulphur status of fertilized trees and significantly increased the weight of fascicles produced during the first year after treatment compared with that achieved with nitrogen alone. Ammonium sulphate was a superior sulphur source compared with elemental sulphur - sodium bentonite prills and also was readily taken up by trees. The oxidation of the elemental sulphur prills was apparently too slow to satisfy sulphur requirements in the first year. Increasing the sulphur application rate from 50 to 100 kg/ha generally gave only small improvements in first-year fascicle weight response despite a significant improvement in foliar sulphur concentration and content. The responsiveness to sulphur fertilization was not consistent across all sites. Further characterization of sites that are responsive and unresponsive to sulphur additions is needed to more accurately diagnose sulphur deficiencies and predict responsiveness to sulphur additions.