The reclamation of bracken-dominated pastures in Bulgaria using asulam and fertilizers

Bracken (Pteridium aquilinum) is a major weed of considerable economic concern in upland pastures in Bulgaria and elsewhere in Europe. Between 1993 and 1998, a field experiment was carried out to rest methods for restoring productive meadows. Initially, spraying asulam (4.8 kg a.i. ha(-1)) was used ro control the bracken on the sire; this was achieved in terms of reduced frond densities and a higher level of grassland establishment. This grassland was dominated by Vicia cassubica and the perennial grasses Agrostis vulgaris, Dactylis glomerata, Festuca rubra. Holcus lanatus and Poa pratensis. After 2 years, a fertilizer addition experiment was started with four treatments (no fertilizer; addition of phosphorus: addition of nitrogen and phosphorus: addition of nitrogen, phosphorus and potassium. The phosphorus and potassium fertilizers were applied annually in the early spring at 80 kg of P ha(-1) year(-1) and 50 kg of K ha(-1) year(-1), and nitrogen was added at the start of grass growth at 60 kg of N ha(-1) year(-1). Ar the same time, a twice-yearly hay-cutting regime was implemented. Fertilizer addition increased both the quantity and the quality of the resulting grassland. The herbage dry matter was increased by at least a factor of two depending on fertilizer combination, and there was an increase in grass and legume cover and a decrease in both weed cover and bracken recovery. However, although bracken recovery was inversely related to grassland production, there was a consistent increase in bracken density across all treatments between 1997 and 1998, suggesting that increasing herbage biomass merely delays bracken recovery. The implications of these findings are discussed.