# Interactive Estimation of van Genuchten's (1980) Model Parameters

### Description

An interactive graphical adjustment of the soil water retention curve via van Genuchten's (1980) formula. The nonlinear least-squares estimates can be achieved taking the graphical initial values.

### Usage

1 | ```
fitsoilwater(theta, x, xlab = NULL, ylab = NULL, ...)
``` |

### Arguments

`theta` |
a numeric vector containing the values of soil water content. |

`x` |
a numeric vector containing the matric potential values. |

`xlab` |
a label for the x axis; if is NULL, the label "Matric potential" is used. |

`ylab` |
a label for the y axis; if is NULL, the label "Soil water content" is used. |

`...` |
further graphical arguments; see |

### Value

A plot of `theta`

versus `x`

and the curve of the current fitted model
according to the adjusted parameters in an external interactive panel.
Pressing the button "NLS estimates" a `nls`

summary of the
fitted model is printed on console whether convergence is achieved, otherwise
a warning box of "No convergence" is shown.

### Author(s)

Anderson Rodrigo da Silva <anderson.agro@hotmail.com>

### References

Genuchten, M. T. van. (1980). A closed form equation for predicting the
hydraulic conductivity of unsaturated soils. *Soil Science Society of
America Journal*, 44:892-898.

### See Also

`nls`

, `soilwater`

### Examples

1 2 3 4 5 6 | ```
# Liu et al. (2011)
h <- c(0.001, 50.65, 293.77, 790.14, 992.74, 5065, 10130, 15195)
w <- c(0.5650, 0.4013, 0.2502, 0.2324, 0.2307, 0.1926, 0.1812, 0.1730)
fitsoilwater(w, h)
# End (not run)
``` |