agridat (version 1.8.1)

kempton.competition: Sugar beet trial with competition effects

Description

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

source

R Kempton, 1982. Adjustment for competition between varieties in plant breeding trials, Journal of Agricultural Science, 98, 599-611.

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.

Examples

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
require("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)

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

# Variance of yield increases with yield
plot(m1)