Calculating “Hydrothermal time” to quantify seed germination of tall fescue

Abstract

The objective of this study was to quantify the combined effects of temperature and moisture on germination of tall fescue seed. Seeds were incubated for up to 50 days at a range of constant temperatures (5-35ºC) and germinated at five water potentials (0, -0.18, -0.37,-0.63 and -0.95 MPa). The maximum final germination percentages were 94 to 98 at 15-30ºC when water was not limited (0 MPa). Germination rate increased linearly from 5 to 27.5ºC, and then decreased linearly from 27.5 to 32.5ºC. Extrapolation of the sub-optimal temperatures identified a base temperature of 3.5 ± 0.5ºC and an optimum temperature of 27.5ºC. More negative water potential indicative of drier conditions, delayed germination and reduced germination rate. The average base water potential was -0.95 MPa at the sub optimal range of temperatures. An optimum range of germination (80-100%) occurred when temperatures were between 10 and 30ºC and water potential was between 0 to -0.37 MPa (moderate stress). These results provide a matrix of soil temperature and moisture conditions that are expected to result in successful germination and therefore provide the maximum opportunity for emergence of tall fescue seedlings.