NUTRIENT LIMITATION AFTER LONG-TERM NITROGEN-FERTILIZER APPLICATION IN CUT GRASSLANDS

1. Current agricultural overproduction in Western Europe has led to an increase of abandoned (unfertilized) grasslands. This paper reports on an experiment where, under hay-making conditions, such a man-made grassland has been N-fertilized (50 kg ha-1 year-1) in order to increase the extraction of nutrients other than N. 2. Above-ground standing crop and soil chemical characteristics of the N-fertilized field were studied in comparison with an unfertilized control for 17 years. After 10-11 years, the twofold higher above-ground 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. 3. 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, not 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. 4. 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.