The effect of photoperiod and temperature on the first crop and ratoon growth of Pennisetum purpureum Schum

Abstract

Elephant grass (Pennisetum purpureum Schum.) was grown in phytotron cabinets for 60 days at 30/25° or 21/16°C (daylnight) in either 8 or 16 hr photoperiods. During the juvenile phase the higher temperature increased the leaf appearance rate, tillering rate and main stem elongation rate. Once plants in the 8 hr photoperiod became reproductive, the stem elongation, tillering rate and leaf appearance rate increased. The higher temperature continued to stimulate development. At harvest at 60 days plants grown at 30/25° had higher leaf, stem and total dry matter yields, a greater leaf area but lower carbohydrate content in the stubble. The 16 hr photoperiod produced higher dry matter yields at harvest than the 8 hr photoperiod. A comparison pot experiment grown in short day and long day photoperiods under field conditions in north Queensland produced similar findings to the phytotron experiment. After harvest, stubbles were ratooned into either short day (8 hr) or long day (16 hr) photoperiods, the temperature difference being maintained. Leaf number per main stem and main stem elongation were similar to those of the first crop, but more tillers and higher yields were produced in the ratoon crop. Temperature and photoperiod effects were similar in both crops. It was concluded that low temperatures rather than reduced photoperiod would be the greatest limitation to the adaptation of the species as an industrial or forage crop where yearround production is required.