Foliar nutrient and tree growth response of mixed-conifer stands to three fertilization treatments in northeast Oregon and north central Washington

The results of two studies evaluating nutrient uptake in mixed-conifer stands following fertilization are reported. The four species examined were Douglas-fir, grand fir, lodgepole pine and ponderosa pine. The fertilization treatments were 224 kg ha^-1 nitrogen, 224 kg ha^-1 nitrogen plus 112 kg ha^-1 sulfur, and 224 kg ha^-1 nitrogen plus 190.4 kg ha^-1 potassium. Foliar nutrient concentrations, contents and ratios were analyzed, as well as four-year volume response. Douglas-fir showed both N and S deficiencies in control foliage samples, and produced significant growth response to the N + S treatment, but not to the N-alone treatment. Grand fir also showed foliar N and S deficiencies, but produced significant growth response to both N and N + S fertilization. This suggests that grand fir was better able to utilize N than Douglas-fir even under S-limiting conditions. Lodgepole pine showed deficient foliar N and S concentrations, and produced significant volume responses to N and N + K fertilization. Lodgepole volume response to N + S fertilization was highly variable, and appeared to be site-specific. Ponderosa pine did not show nutrient deficiencies for N or K, and did not respond significantly in either foliar K or S levels or in growth to N, N + K or N + S fertilization. This suggests that nutrient deficiency may not have been a factor limiting foliar nutrient response and growth for ponderosa pine. (C) 2000 Elsevier Science B.V.