WEATHERING LOSSES OF FORAGE SPECIES ON THE FESCUE GRASSLAND IN SOUTHWESTERN ALBERTA

Rough fescue grasslands are readily damaged by heavy grazing pressure in the summer but tolerate grazing in winter. The grasslands have phys ical and nutritive properties that make them suitable for winter grazi ng by cattle thereby reducing the cost of winter feeding while preserv ing the integrity of the grasslands. However, their forage value decli nes during winter through the degradation of biomass yield and quality . This study look place at the Agriculture and Agri-Food Canada, Range Research Substation located on the Porcupine Hills in southwest Alber ta. The objectives of this study were to determine the dynamics of lit ter biomass for important forage species over winter, to examine the r ole of leaf position in the plant on biomass loss from leaves, and to determine the associated changes in crude protein, phosphorus, and aci d detergent fibre of the leaves, and carbon and nitrogen. Leaves of Pa rry oat grass (Danthonia parryi Scribn.), Idaho fescue (F. idahoensis Elmer), and rough fescue (F. campestris Rydb.) were sampled at monthly intervals from August to March over 3 yr to determine weight and chem ical composition. Decomposition of these species, together with smooth aster (Aster laevis L.), was also tested for decomposition in the lit ter mass using nylon bags. Degradation of standing litter was most rap id in late summer and tended to decline toward stability by December. Biomass losses in leaves from August to March were similar (P > 0.05) among grass species. Overwinter losses in the litter mass tended to be greatest for smooth aster. Changes in the mineral and fibre concentra tions of the herbage were typical of the trends expected for the perio d, that included late senescence and weathering, and followed closely the losses of biomass for the period. Forage decomposition is an impor tant ecological process in mineral cycling and affects the quantity an d quality of forage available for delayed grazing.