Factors affecting the growth of Pennisetum purpureum in the wet tropics. I. Short-term growth and regrowth

Abstract

Six plantings of elephant grass (Pennisetum purpureurn) were made at 2-monthly intervals in the wet tropics of north Queensland. Each crop was sampled for yield at monthly intervals. After 6 months' growth each crop was ratooned for a further 6 months' growth, with yield samples again being taken at monthly intervals. As well, stem elongation growth was measured twice weekly, together with various climatic parameters and soil moisture to 90 cm. Regrowths after each monthly harvest were sampled 1 month after cutting. Short-term growth, measured as elongation growth and averaged for the whole experimental period, was found to have a significant parabolic relationship with crop age and available soil moisture percentage, but not with average temperature or evaporation. Regrowth yields were found to be linearly and positively correlated with tiller density prior to ratooning and regrowth tiller density, with average regrowth temperature or regrowth degree days but linearly and negatively correlated with moisture regime, whether expressed as average parent-crop soil moisture prior to harvest, average regrowth soil moisture percentage or the summation of stress-free days. It was concluded that environmental limitations to growth in this environment, though relatively short lived, were significant in reducing long-term yields. Growth, however, was possible at all times.