NUTRIENT SUPPLY AND FERTILIZER EXPERIMENTS IN VIEW OF N-SATURATION

New types of forest damage associated with Mg (and K) deficiency can be corrected by proper fertilization using fast release Mg (and K) fertilizers or Mg limestone. Sufficient Mg and K supply provided by former fertilizer applications inhibited the appearance of typical deficiency symptoms in areas where unfertilized control trees are now characterized by yellowing. In these areas N input rates vary appreciably. Addition of N fertilizers, particularly in the form of NH4-N, can induce nutrient imbalances as was demonstrated for Mg and K. From these disorders relative growth reductions may result. However, sustained negative effects will probably only occur when large doses are applied or when atmospheric N input rates are high. Increased N uptake due to N fertilization indicated that the investigated sites were not saturated with N. Needle analysis is a very simple as well as valuable tool to characterize the nutritional status of forest tress and stands when it is carried out correctly. Nutrient ratios should receive the attention they deserve, rather than concentrate exclusively on the evaluation of absolute nutrient contents. © 1990 Kluwer Academic Publishers.