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, ...)

Arguments

data dataframe or matrix
... Parameters of the plot()

Details

$V_{x}=frac{V_{(x)}}{x^b}$

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

data Numeric

...

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 1.0-6 Index]