Potential uses of bracken (Pteridium aquilinum (L.) Kuhn) in organic agriculture in Scotland
To assess the availability of bracken and the factors influencing frond yields, this thesis investigated the growth and phenology of bracken populations across Scotland in relation to site characteristics. The change in elements in fronds and litter from April to November was analysed, along with the concentrations of the carcinogen Ptaquiloside (Pta). Frond dry matter yields increased to maximum in August/September, falling to those in November. In September/October, frond yields ranged from 4.70-15.9 DM t ha-1. Frond concentrations of phosphorus and potassium reduced, and concentrations of calcium and magnesium increased from May to November. Frond Pta concentrations reduced during this period also, with the highest concentration recorded of 5792 mg kg-1 in May 2002 at Loch Grannoch, SW Scotland. This thesis also investigated the effects of harvesting of fronds, and the burning and clearing of litter on the yield of frond dry matter, yield and content of ash and on Pta concentrations in fronds. The concentration of twenty-one elements, the CaCO3 equivalence and pH of this ash were determined, and the effect of harvesting of fronds on subsequent yields was assessed. Harvesting during the growing season reduced the preceding yield of fronds, but not if harvested after senescence. A positive regression was found between frond DM and ash yields. The maximum yield of K in ash was harvested in August/September, at around 180 kg ha-1. Calculations of the value of bracken ash using August 2001 K concentrations and the cost of other organic K sources came to between £219-£980 t-1. The ash produced had a mean pH of 11.9, and mean calcium carbonate equivalence of 52%. Lifting litter increased the density of fronds, and burning litter increased the soil available Mg concentrations and Ca concentrations in the ash. Pta concentrations in fronds that emerged in reaction to harvesting were higher compared to those fronds first harvested at the same time.