Lodgepole Pine Fertilization Screening Trials: Four‐year Growth Response Following Initial Predictions

The use of fertilizer screening trials was examined to determine if the pattern of 4‐yr basal area (BA) increment response by treatment agreed with the predictions based on first season needle weight response. Screening trials can diagnose stand nutritional status and subsequent response. Nitrogen, P and K in various combinations were applied to 17 lodgepole pine ( Pinus contorta var. latifolia Engelm.) stands in the interior of British Columbia, Canada. Of these, 14 had been precommercially thinned. Remeasurement of 15 stands after 4 yr showed that 50 to 150 kg N ha −1 produced significant growth responses in many stands. Nitrogen applied at rates of 50, 100, and 150 kg ha −1 increased BA growth of individual trees by an average of 27, 41, and 48% over the control, respectively. Adding P at 50 kg ha −1 significantly improved BA growth in only two stands, while the effect of K was not significant. Graphical diagnoses of shifts in unit fascicle weight and foliar concentrations and contents in the first growing season following fertilization generally corresponded with subsequent 4‐yr BA response in 11 of the 15 installations. Stands responsive to N fertilization were weakly responsive to thinning. Nonresponsive stands reacted to thinning, presumably because N was not limiting growth. The best fit of multiple regression analyses between basal area response and stand factors yielded an R 2 of 0.57, with needle weight and foliar N and P levels as important variables.