Sugar beet trial with competition effects

Yield of sugar beets for 36 varieties in a 3-rep RCB experiment. Competition effects are present.

Format

A data frame with 108 observations on the following 5 variables.

gen

genotype, 36 levels

rep

rep, 3 levels

row

row

col

column

yield

yield, kg/plot

Details

Entries are grown in 12m rows, 0.5m apart. Guard rows were grown alongside replicate boundaries, but yields of these plots are not included.

Source

R Kempton, 1982. Adjustment for competition between varieties in plant breeding trials, Journal of Agricultural Science, 98, 599-611. https://doi.org/10.1017/S0021859600054381

Examples

if (FALSE) { # \dontrun{
  
library(agridat)

data(kempton.competition)
dat <- kempton.competition

# Raw means in Kempton table 2
round(tapply(dat$yield, dat$gen, mean),2)

# Fixed genotype effects, random rep effects,
# Autocorrelation of neighboring plots within the same rep, phi = -0.22
libs(nlme)
m1 <- lme(yield ~ -1+gen, random=~1|rep, data=dat,
          corr=corAR1(form=~col|rep))
# Lag 1 autocorrelation is negative--evidence of competition
plot(ACF(m1), alpha=.05, grid=TRUE, main="kempton.competition",
     ylab="Autocorrelation between neighborning plots")

# Genotype effects
round(fixef(m1),2)

# Variance of yield increases with yield
plot(m1, main="kempton.competition")

} # }