Description Usage Arguments Details Value Note Author(s) References See Also Examples

Richards equation (Richards, 1959) J Exp Bot 10: 290-300. This is equation 2.2 in Table 1 in the paper referenced below (Archontoulis and Miguez).

1 |

`time` |
a numeric vector of values at which to evaluate the model. |

`tmax` |
tmax is the time when growth rate is maximum |

`theta` |
thetha determines the curvature. The relative growth rate is RGR = theta/(1+v). |

`v` |
v parameter determines the asymetrical growth. |

`Yo` |
Yo is the max Y |

Richards equation is an extension of the logistic to deal with asymmetrical growth.

a numeric vector of length equal to the inputs

Applied to describe water stress index, crop N-uptake, seed germination, crop growth, LAI development, etc. Remark at time = 0, Y is not zero Richards equation has often been criticized because the shape parameter v has no obvious biological interpretation

Fernando Miguez

Richards equation (Richards, 1959) J Exp Bot 10: 290-300

Nonlinear Regression Models and Applications in Agricultural Research. Sotirios V. Archontoulis and Fernando E. Miguez. Agronomy Journal. doi: 10.2134/agronj2012.0506

There used to be an R package called richards but it is no longer maintained.

1 2 3 4 5 6 7 8 | ```
require(lattice)
time <- seq(0, 150,5)
ans1 <- rich(time, tmax = 60, theta = 0.07, v=1.3, Yo=100)
ans2 <- rich(time, tmax = 60, theta = 0.07, v=0.6, Yo=100)
ans3 <- rich(time, tmax = 60, theta = 0.07, v=0.3, Yo=100)
ans4 <- rich(time, tmax = 60, theta = 0.07, v=1.0, Yo=100)
xyplot(ans1 + ans2 + ans3 + ans4 ~ time,
type="l", auto.key=TRUE, ylab = "text", xlab = "time")
``` |

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