Buffering Capacities in Permanent Pasture Grasses

Abstract

Buffering capacity, as affected by maturity and season, was measured in grass harvested from two permanent pastures, which varied in botanical composition. Primary growth and summer regrowths were harvested from one plot per block weekly from the vegetative through completely headed stages. Autumn regrowth was harvested every two weeks from 7 September to 19 October. Buffering capacities in both pastures were similar for a given harvest date. During primary growth and subsequent summer regrowth, buffering capacity declined on average 20 meq/kg DM per week, starting at approximately 400-450 meq/kg DM for vegetative grass, two to three weeks before the emergence of seed heads. Autumn regrowth (September-October) remained vegetative and buffering capacity was relatively constant (350-450 meq/kg DM). Correlations of buffering capacity with water-soluble carbohydrates and nitrate were poor whereas those with crude protein (CP) and in vitro dry matter digestibility (IVDMD) were strong. However, with high and medium quality grass, the buffering capacity of primary growth at a given CP or IVDMD content was higher than that of regrowth.