The effects of temperature and water potential on the germination of sorghum
Poor or failed crop establishment is a serious problem for farmers in the semi-arid tropics. Suboptimal stand densities or the necessity to re-sow can be a major factor in limiting crop yields. Establishment can be considered as the result of a set of complex interactions between the seed, the soil and the climate. The experiments detailed within this volume were carried out to determine parameters for sorghum germination for a model to predict crop emergence in the semi-arid tropics to aid the greater understanding of the causes of establishment problems. The cumulative germination of sorghum cv. Tegemeo was recorded in conditions of both constant temperatures and fluctuating temperatures on a thermogradient plate and at negative water potentials over a range of temperatures in solutions of polyethylene glycol and in soil. Results demonstrate that within a temperature range of 14 - 40oC germination can be predicted using a thermal time model. The effect of temperature fluctuation on the time to germination within this temperature range can be predicted using the same thermal time constants that model behaviour at constant temperatures. Prediction of the time to germination in soil using a hydrothermal model (Gummerson 1986) was found to be accurate over a wide range of temperatures (15 - 35oC) and soil matrix potentials (0 - -0.6 MPa). The results of this study have been incorporated into "EMERGE" (Mullins et al., 1996), a published crop emergence model. The potential use of hydrothermal modelling as a tool to investigate aspects of seed vigour is discussed.