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 1.2-9 Index]