EFFECTS OF NITROGEN, PHOSPHORUS AND POTASSIUM FERTILIZATION ON FIELD PERFORMANCE OF DACTYLORHIZA-MAJALIS

The effects of nitrogen, potassium and phosphorus fertilization on per formance of Dactylorhiza majalis (Rchb.f.) Hunt & Summerh. were studie d in a Juncus acutiflorus-dominated hayfield. Frequency, total shoot b iomass and flowering incidence decreased as a result of both nitrogen and phosphorus application. Nutrient additions also affected yields of species showing positive and negative association with orchid perform ance. These changes were sufficient in explaining the nitrogen and pho sphate response of orchid shoot biomass and extent of flowering. The m ost important competitors in this respect were Rumex acetosa and Holcu s lanatus. The negative overall N- and P-effect on orchid frequency se emed to be independent of changes in the surrounding vegetation howeve r. The relative importance of nutrient limitations and additions is di scussed in relation to the species decline in frequency and to its rea ppearance in grasslands under restoration management with decreasing n utrient availability.