agricolae (version 1.2-8)

index.smith: 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()

Value

model

function pattern of uniformity

uniformity

Table of the soil uniformity

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.

References

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

Examples

# NOT RUN {
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
# }