Weathering losses of forage species on the fescue grassland in southwestern Alberta

Abstract

Rough fescue grasslands are readily damaged by heavy grazing pressure in the summer but tolerate grazing in winter. The grasslands have physical and nutritive properties that make them suitable for winter grazing by cattle thereby reducing the cost of winter feeding while preserving the integrity of the grasslands. However, their forage value declines during winter through the degradation of biomass yield and quality. This study took place at the Agriculture and Agri-Food Canada, Range Research Substation located on the Porcupine Hills in southwest Alberta. The objectives of this study were to determine the dynamics of litter biomass for important forage species over winter, to examine the role of leaf position in the plant on biomass loss from leaves, and to determine the associated changes in crude protein, phosphorus, and acid detergent fibre of the leaves, and carbon and nitrogen. Leaves of Parry 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 chemical composition. Decomposition of these species, together with smooth aster (Aster laevis L.), was also tested for decomposition in the litter mass using nylon bags. Degradation of standing litter was most rapid 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. Over-winter losses in the litter mass tended to be greatest for smooth aster. Changes in the mineral and fibre concentrations of the herbage were typical of the trends expected for the period, that included late senescence and weathering, and followed closely the losses of biomass for the period. Forage decomposition is an important ecological process in mineral cycling and affects the quantity and quality of forage available for delayed grazing. Key words: Standing litter, buried litter, biomass, forage quality, winter, Parry oat grass, Idaho fescue, rough fescue, smooth aster