Seasonal variations in total nonstructural carbohydrate and major element levels in perennial ryegrass and paspalum in a mixed pasture

Abstract

In the first of two experiments, above-and below-ground organs of paspalum (Paspalum dilatatum Poir.) and ryegrass (Lolium perenne L.) growing in a mixed dairy pasture were sampled over 12 months and their total nonstructural carbohydrate (soluble sugars and starch) and major element (N, P, K, S, Mg, Na) concentrations were determined. In the second experiment, biomass of ryegrass and paspalum were monitored over 12 months. Pasture biomass was dominated in all seasons by paspalum, primarily because of the size of its below-ground rhizome which more than doubled from December (1.6 t dry matter (DM)/ha to May (4.4 t DM/ha) coinciding with an increasing concentration (6-19% of DM) of nonstructural carbohydrates. In contrast, nonstructural carbohydrate concentrations in ryegrass were highest (13% of DM) in above-ground organs (leaves and “stems”) during winter followed by a decline before heading in spring. Seasonal variations in elemental concentrations in ryegrass organs were small. This was also true for paspalum leaves and roots but rhizome and “stem” nitrogen concentrations during autumn, winter, and early spring were almost double their summer levels of about 2% of DM. Paspalum had a larger total biomass and more reserves Received 21 September 1987; accepted 11 January 1989 than ryegrass. Climatic and management constraints which reduce ryegrass biomass and reserves may increase ryegrass mortality and the pasture area occupied by paspalum.