Effects of nitrogen, phosphorus and potassium fertilization on field performance of Dactylorhiza majalis

The effects of nitrogen, potassium and phosphorus fertilization on performance of Dactylorhiza majalis (Rchb.f.) Hunt & Summerh. were studied in a Juncus acutiflorus-dominated hayfield. Frequency, total shoot biomass 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 performance. These changes were sufficient in explaining the nitrogen and phosphate response of orchid shoot biomass and extent of flowering. The most important competitors in this respect were Rumex acetosa and Holcus lanatus. The negative overall N- and P-effect on orchid frequency seemed to be independent of changes in the surrounding vegetation however. The relative importance of nutrient limitations and additions is discussed in relation to the species decline in frequency and to its reappearance in grasslands under restoration management with decreasing nutrient availability.