bradford: Fits Bradford's hydrotime model

In seedr: Hydro and Thermal Time Seed Germination Models in R

Description

bradford fits a hydrotime seed germination model using the method of Bradford (Gummerson 1986, Bradford 1990, Bewley et al. 2013). This function can be used only with one-group dataset, i.e. one seed lot of one species. To fit models to grouped datasets (multi-seedlots, multi-species) use the function physiotime instead.

Usage

bradford(d)

Arguments

d	a data.table within a "physiodata" object, containing the cumulative germination proportion at each scoring time and water potential treatment.

Value

bradford returns a S3 object of class "bradford" with the results of fitting the hydrotime model. The generic functions summary and plot are used to obtain and visualize the model results.

References

Bewley, J. D., Bradford, K. J., Hilhorst, H. W., & Nonogaki, H. (2013). Hydrotime Model of Germination. In Seeds: Physiology of Development, Germination and Dormancy, 3rd Edition (pp. 303-307). Springer, New York, NY.

Bradford, K. J. (1990). A water relations analysis of seed germination rates. Plant Physiology, 94(2), 840-849.

Gummerson, R. J. (1986). The effect of constant temperatures and osmotic potentials on the germination of sugar beet. Journal of Experimental Botany, 37(6), 729-741.

Examples

# format dataset with physiodata
anisantha <- physiodata(subset(grasses, species == "Anisantha rubens"), x = "psi")
# bradford() uses the $proportions element within the physiodata object
b <- bradford(anisantha$proportions)
b # prints the main hydrotime variables
summary(b) # returns the main hydrotime variables as a data.table
plot(b) # plots the fitted model

Example output

Bradford's hydrotime model 
 Water potential levels in experiment: -1.6 -1 -0.8 -0.6 -0.4 -0.2 0 
 Theta - Hydrotime constant: 50.54 
 Psib50 - Base water potential (median): -1.59 
 Sigma of the base water potential: 0.4 
 R2: 0.94 
 
     method n.treatments    theta    psib50    sigma        R2
1: bradford            7 50.54104 -1.591533 0.395942 0.9419596

seedr documentation built on Nov. 8, 2020, 4:29 p.m.