Current issue: 56(3)
Multivariate methods are used to classify pine mires on the basis of edaphic properties into fertility groups in order to estimate the effect of fertilization in relation to site fertility. The data is based on two field inventories of NPK fertilization experiment in which 2,624 sample trees on 164 sample plots from 19 experimental fields were measured on Scots pine (Pinus sylvestris L.) dominated stands. The edaphic properties (total contents of nutrients and related properties) are based on 1,350 volumetric sub-samples of fertilized and non-fertilized control plots.
In a DECORANA ordination, based on standardised volumetric soil variables N-P and acid-base gradients jointly describing trophic status were distinguished. Mainly on the basis of these two gradients a TWINSPAN analysis divided the material into five edaphic groups. To independently allocate sample plots into fertility groups, discriminating multiple regressions were formed using the TS edaphic groups as class variable.
The effect of N, P, K, NP, NK, PK, and NPK treatments on tree growth was estimated on the basis of change in relative basal area increment during two growth periods. During five-year period immediately after fertilization N and P treatments evoked the strongest increase in growth. On the nutrient poor sites, the effect was almost double that on the fertile sites. The effect of N was short lasting while the P treatment still affected growth after 5–11 years. Although K treatment had little influence on tree growth needle samples collected 11 years after fertilization indicated increased K uptake on fertilized plots.
Generally, the effect of fertilization on absolute stand volume growth was small. During the 11-year study period the total increase in growth gained with NPK was some 3–4 m3/ha. Despite strong relative response of individual sample trees, due to low stand volume fertilization (and drainage) had practically no effect on volume growth on the sites of lowest fertility.
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