Effect of clipping interval and nitrogen fertilisation on oxalate content in pot-grown napier grass (Pennisetum purpureum)

摘要

Tropical grasses sometimes contain oxalate in sufficient concentrations to induce calcium deficiency and toxicity in grazing animals. This pot study was undertaken to investigate the effects of clipping interval and N fertilisation on the oxalate concentrations in napier grass. Plants were treated with 2 rates (5 and 30 g/m~2) of N fertiliser (as urea) and harvested at 3 clipping intervals (2, 4 and 8 weeks). At all clipping intervals, both forage dry matter yield and crude protein concentration in the forage were greater (P<0.05) with the higher N fertiliser rate than with the lower rate. Clipping increased oxalate concentration (P<0.05), and oxalate levels declined as the harvest interval increased. Across all clipping regimes, concentrations of soluble (15.2 vs 14.9 g/kg DM), insoluble (11.1 vs 12.0 g/kg DM) and total (26.3 vs 26.8 g/kg DM) oxalates in the plant tissues were not affected significantly (P>0.05) by level of N fertiliser applied. These results suggest that N fertilisation using urea at the levels we used will not result in elevated oxalate levels in napier grass. Harvesting at 8-weekly intervals will lower oxalate concentrations without resulting in low CP levels, provided moderate N fertiliser rates are used.