ryegrass                 package:drc                 R Documentation

_E_f_f_e_c_t _o_f _f_e_r_u_l_i_c _a_c_i_d _o_n _g_r_o_w_t_h _o_f _r_y_e_g_r_a_s_s

_D_e_s_c_r_i_p_t_i_o_n:

     A single dose-response curve.

_U_s_a_g_e:

     data(ryegrass)

_F_o_r_m_a_t:

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

     _r_o_o_t_l a numeric vector of root lengths  

     _c_o_n_c a numeric vector of concentrations of ferulic acid

_D_e_t_a_i_l_s:

     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.

_S_o_u_r_c_e:

     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.

_E_x_a_m_p_l_e_s:

     ## 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)

