Stands of millet were grown in temperature-controlled glasshouses maintained at mean air temperatures of 19-31 °C and sub-plots were heated or cooled to examine the effect of soil temperature on early plant development.
Soil temperature influenced all aspects of early vegetative development: the emergence of seedlings, the initiation, appearance and final number of leaves and tillers. Results are presented in terms of both chronological and ‘thermal’ time (the summation of degree days (°C d) above an extrapolated base (Tb) determined from the rate/temperature relation). Rates of the processes examined increased linearly with temperature, but the duration of vegetative phases appeared to be constant between 19-30 °C. The rate of all processes can therefore be described by a specific thermal time (Θ) e. g. 26 °C d for each leaf initiated and a base temperature (Tb) which was similar for all the vegetative processes examined. 0 was relatively constant over the range of irradiance and saturation deficit experienced in the experiments.
The results are compared to previous data for millet and other tropical species.