The interactive effects of management on the productivity and plant community structure of an upland meadow: an 8-year field trial

1. Agricultural policy in the Pennine Dales Environmentally Sensitive Area in northern England aims to enhance plant species diversity in agricultural ly improved meadows and return them to a 'traditional' species composition. The interacting effects of management on vegetation and productivity were tested in a split-split-split plot experiment. Three grazing treatments (au tumn grazing with cattle and sheep, spring grazing with sheep. both regimes ) were applied between 1990 and 98. Two fertilizer treatments (25 kg ha(-1) N plus 12.5 kg ha(-1) P2O5 and K2O, no fertilizer): three hay cut date tre atments (14 June, 21 July, 1 September) and two seed addition treatments (n o seed, seed of many species) were used within the grazing treatments. 2. By 1998, all the main treatments had produced small but significant chan ges to plant species diversity. A particularly large increase in diversity occurred with the combination of autumn and spring grazing. 21 July hay cut date and seed addition treatments. This change was achieved by an episodic rather than a regular increase in species over time. 3. Rhinanthus minor spread to most plots after its introduction as a consti tuent of the seed treatment. By 1996 it was particularly abundant in all tr eatment combinations that included autumn grazing, no mineral fertilizer an d a July haycut. Populations of > 40 plants m(-2) were associated with the lowest yields of hay. 4. 'Unimproved-traditional' plant communities, mainly Festuca ovina-Agrosti s capillaris-Galium saxatile grassland, occupied more than 66% of the trial area. Anthoxanthum odoratuam-Gerantium sylvaticum grasslands were most abu ndant in 1996, being primarily associated with the combination of autumn an d spring grazing, 21 July and September hay cut dates and seed addition tre atments, over both fertilizer treatments. 5. Yields of herbage biomass initially declined over time in all treatment combinations. Lowest yields in most years were associated with the autumn a nd spring grazing, 14 June cutting date and no fertilizer treatments. 6. Management to increase the number of plant species in agriculturally imp roved mesotrophic grassland requires the joint implementation of appropriat e cut date and grazing regimes, probably to provide regeneration niches, an d the application of seed to provide species to fill these niches. The smal l amount of mineral fertilizer used in this experiment had a measurable eff ect, but was of lesser importance.