Use of a simple distribution function to estimate germination rates and thermal time requirements for seed germination in cool-season herbage species
An exponential distribution with a lag phase was considered for the concise and practical estimation of germination rates in the determination of the base temperature and thermal time required for seed germination. The germination time courses of nine herbage species (Italian ryegrass, perennial ryegrass, timothy, cocksfoot, tall fescue, Kentucky bluegrass, red clover, white clover, and lucerne) were examined at seven constant temperatures (5, 10, 15, 20, 25, 30, and 35°C), and then used for the nonlinear fitting of this distribution to estimate the mean and median durations until seed germination. The distribution showed excellent goodness of fit to the observed germination time course for any combination of herbage species and temperatures (root mean square of residuals, RMSR ≤ 0.0903). Two germination rates as the reciprocals of the estimated mean and median durations, which are denoted by V μ and V m, were linearly regressed with respect to temperature to determine the base temperature and thermal time. The linear regression showed excellent goodness of fit in all examined herbage species (correlation coefficient, r > 0.975). The ranges of base temperatures and thermal times in the examined herbage species were from 0.234 to 4.48°C and from 14.9 to 176 degree days calculated using V μ , and from 0.191 to 4.26°C and from 13.6 to 152 degree days calculated using V m, respectively. The results differed little from those of existing studies on the thermal time for the seed germination of cool-season herbage species, indicating that the exponential distribution with a lag phase is useful for the estimation of seed germination rate.
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Document Type: Research Article
Publication date: October 1, 2010
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