drc (version 2.5-12)

ryegrass: Effect of ferulic acid on growth of ryegrass

Description

A single dose-response curve.

Usage

data(ryegrass)

Format

A data frame with 24 observations on the following 2 variables.

rootl

a numeric vector of root lengths

conc

a numeric vector of concentrations of ferulic acid

Source

Inderjit and J. C. Streibig, and M. Olofsdotter (2002) Joint action of phenolic acid mixtures and its significance in allelopathy research, Physiologia Plantarum, 114, 422--428, 2002.

Details

The data are part of a study to investigate the joint action of phenolic acids on root growth inhibition of perennial ryegrass (Lolium perenne L).

conc is the concentration of ferulic acid is in mM, and rootl is the root length of perennial ryegrass measured in cm.

Examples

## Displaying the data set
ryegrass

## Fitting a four-parameter Weibull model (type 2)
ryegrass.m1 <- drm(rootl ~ conc, data = ryegrass, fct = W2.4())

## Displaying a summary of the model fit
summary(ryegrass.m1)

## Plotting the fitted curve together with the original data
plot(ryegrass.m1)

## Fitting a four-parameter Weibull model (type 1)
ryegrass.m2 <- drm(rootl ~ conc, data = ryegrass, fct = W1.4())
plot(ryegrass.m2)

## Fitting a four-parameter log-logistic model
## with user-defined parameter names
ryegrass.m3 <- drm(rootl ~ conc, data = ryegrass, 
fct = LL.4(names = c("Slope", "Lower Limit", "Upper Limit", "ED50")))
summary(ryegrass.m3)

## Comparing log-logistic and Weibull models
## (Figure 2 in Ritz (2009))
ryegrass.m0 <- drm(rootl ~ conc, data = ryegrass, fct = LL.4())
ryegrass.m1 <- drm(rootl ~ conc, data = ryegrass, fct = W1.4())
ryegrass.m2 <- drm(rootl ~ conc, data = ryegrass, fct = W2.4())

plot(ryegrass.m0, broken=TRUE, xlab="Dose (mM)", ylab="Root length (cm)", lwd=2, 
cex=1.2, cex.axis=1.2, cex.lab=1.2)
plot(ryegrass.m1, add=TRUE, broken=TRUE, lty=2, lwd=2)
plot(ryegrass.m2, add=TRUE, broken=TRUE, lty=3, lwd=2)

arrows(3, 7.5, 1.4, 7.5, 0.15, lwd=2)
text(3,7.5, "Weibull-2", pos=4, cex=1.2)

arrows(2.5, 0.9, 5.7, 0.9, 0.15, lwd=2)
text(3,0.9, "Weibull-1", pos=2, cex=1.2)