index.smith {agricolae} | R Documentation |
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.
index.smith(data, ...)
data |
dataframe or matrix |
... |
Parameters of the plot() |
$V_{x}=frac{V_{(x)}}{x^b}$
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.
data |
Numeric |
...
Felipe de Mendiburu
Statistical Procedures for Agriculture Research. Second Edition. Kwanchai A. Gomez and Arturo A. Gomez. 1976. USA
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