The chemical composition of high-sugar and control ryegrasses in grazed pastures at different latitudes throughout New Zealand

摘要

Extrapolating from single-site animal studies of the effects of water soluble carbohydrate (WSC) on methane and nitrogen emissions requires knowledge of geographical and temporal variation in plant chemical constituents. To provide this, samples of grazed pasture were collected from experiments at four different latitudes over one year. At each site, one high-sugar perennial ryegrass (HSG) and two control cultivars of perennial ryegrass, were sampled at each grazing during a 12-month period and analysed for concentrations of WSC, crude protein (CP) and fibre (NDF). Compared with the controls the HSG was higher in WSC (overall mean 299 vs 260 g WSC/kg DM; P<0.01 at each site), lower in NDF (426 vs 460 g NDF/kg DM; P<0.01 at each site) but did not differ in CP. There were significant differences among sites (P<0.001) with highest concentrations of WSC in Canterbury followed by Southland, Waikato and Manawatu (295, 278, 266 and 254 g WSC/kg DM, respectively). Concentrations of WSC were highest in spring and approximately double those in autumn. Animal responses to cultivars with a higher concentration of WSC will be tempered by these large natural variations, which must be accounted for when extrapolating or scaling-up to regional or national outcomes.