# Soil Water Retention, based on the Dexter's (2008) formula

### Description

Function to calculate the soil water content based on the Dexter's (2008) formula. It is based on the segregation of pore space in two categories what are called bi-modal pore size distributions. In this model, the pore space is divided into two parts: the textural porosity which occurs between the primary mineral particles, and the structural porosity which occurs between micro aggregates and/or any other compound particles. This is called the double-exponential (DE) water retention equation, given by:

*θ = θ_R + a_1 \exp(-x/p_1) + a_2 \exp(-x/p_2) *

where *θ* is the gravimetric water content.

### Usage

1 | ```
soilwater3(x, theta_R, a1, p1, a2, p2)
``` |

### Arguments

`x` |
a numeric vector containing the values of applied air pressure. |

`theta_R` |
a parameter that represents the residual water content. |

`a1` |
a parameter that represents the drainable part of the textural pore space in units of gravimetric water content at saturation. |

`p1` |
a parameter that represents the applied air pressures characteristic for displacement of water from the textural pore space. |

`a2` |
a parameter that represents the total structural pore space in units of gravimetric water content at saturation. |

`p2` |
a parameter that represents the applied air pressure that is characteristic for displacing water from the structural pores. |

### Value

The the soil water content.

### Author(s)

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

### References

Dexter et al. (2008). A user-friendly water retention function that takes account of the textural
and structural pore spaces in soil. *Geoderma*, 143:243-253.

### See Also

`fitsoilwater3`

, `soilwater`

, `soilwater2`

### Examples

1 2 3 4 5 | ```
soilwater3(x = 0, theta_R = 0.058, a1 = 0.233, p1 = 3.274, a2 = 0.070, p2 = 1.78)
soilwater3(x = 3, theta_R = 0.058, a1 = 0.233, p1 = 3.274, a2 = 0.070, p2 = 1.78)
soilwater3(x = 4, theta_R = 0.058, a1 = 0.233, p1 = 3.274, a2 = 0.070, p2 = 1.78)
# End (not run)
``` |