Nutrient limitation after long-term nitrogen fertilizer application in cut grasslands.
In a field trial in the Drentsche A Nature Reserve in the Netherlands, a grassland reclaimed from a heathland in 1950 and taken out of agricultural production in 1971 was given 50 kg N/ha annually and dolomitic limestone in Apr. or was given no fertilizers. The vegetation was cut annually and the biomass removed in late July or early Aug. Aboveground standing crop and soil chemical characteristics were studied for 17 years. After 10-11 years, the 2-fold higher aboveground production in the fertilized treatment started to decrease, finally converging with the control. The number of species, however, was still lower in the N-fertilized field compared with the control. After 16 years, no significant differences in soil chemical variables could be established. After 16 years, relative deficiencies of plant available N, P and K were estimated for both fields using several phytometric greenhouse methods. N and K, rather than P, were the most limiting nutrients. A field experiment with factorial fertilizer application showed that the vegetation of the N-fertilized field did not respond to N and P, but responded strongly to K, contrasting with the responses of the vegetation of the control field, which responded to N. The results are discussed with regard to methods of measuring nutrient availability in soils of low fertility, to nature conservation practices and to species richness.