index.smith {agricolae} | R Documentation |

## Uniformity soil. Smith's Index of Soil Heterogeneity

### Description

Smith's index of soil heterogeneity is used primarily to derive optimum plot size. The index gives a single value as a quantitative measure of soil heterogeneity in an area. Graph CV for plot size and shape.

### Usage

```
index.smith(data, PLOT=TRUE,...)
```

### Arguments

`data` |
dataframe or matrix |

`PLOT` |
graphics, TRUE or FALSE |

`...` |
Parameters of the plot() |

### Details

Vx=V(x)/x b

V(x) is the between-plot variance, Vx is the variance per unit area for plot size of x basic unit, and b is the Smith' index of soil heterogeneity.

### Value

`model` |
function pattern of uniformity |

`uniformity` |
Table of the soil uniformity |

### Author(s)

Felipe de Mendiburu

### References

Statistical Procedures for Agriculture Research. Second Edition. Kwanchai A. Gomez and Arturo A. Gomez. 1976. USA

### Examples

```
library(agricolae)
data(rice)
#startgraph
table<-index.smith(rice,
main="Relationship between CV per unit area and plot size",col="red")
#endgraph
uniformity <- data.frame(table$uniformity)
uniformity
# regression variance per unit area an plot size.
model <- lm(Vx ~ I(log(Size)),uniformity)
coeff <- coef(model)
x<-1:max(uniformity$Size)
Vx<- coeff[1]+coeff[2]*log(x)
#startgraph
plot(x,Vx, type="l", col="blue",
main="Relationship between variance per unit area and plot size")
points(uniformity$Size,uniformity$Vx)
#endgraph
```

[Package

*agricolae*version 1.3-7 Index]