agridat (version 1.12)

besag.triticale: Four-way factorial agronomic experiment in triticale

Description

Four-way factorial agronomic experiment in triticale

Usage

data("besag.triticale")

Format

A data frame with 54 observations on the following 7 variables.

yield

yield, g/m^2

row

row

col

column

gen

genotype / variety, 3 levels

rate

seeding rate, kg/ha

nitro

nitrogen rate, kw/ha

regulator

growth regulator, 3 levels

Details

Experiment conducted as a factorial on the yields of triticale. Fully randomized. Plots were 1.5m x 5.5m.

Besag and Kempton show how accounting for neighbors changes non-significant genotype differences into significant differences.

References

None.

Examples

# NOT RUN {
data(besag.triticale)
dat <- besag.triticale

require(lattice)
# desplot(yield ~ col*row, data=dat, main="besag.triticale")

# Besag & Kempton are not perfectly clear on the model, but
# indicate that there was no evidence of any two-way interactions.
# A reduced, main-effect model had genotype effects that were
# "close to significant" at the five percent level.
# The model below has p-value of gen at .04, so must be slightly
# different than their model.
dat <- transform(dat, rate=factor(rate), nitro=factor(nitro))
dat <- transform(dat, xf=factor(col), yf=factor(row))
m2 <- lm(yield ~ gen + rate + nitro + regulator + yf, data=dat)
anova(m2)

# Similar, but not exact, to Besag figure 5
dat$res <- resid(m2)
xyplot(res ~ col|as.character(row), data=dat,
       as.table=TRUE, type="s", layout=c(1,3),
       main="besag.tritical")

# }
# NOT RUN {
  # Besag uses an adjustment based on neighboring plots.
  # This analysis fits the standard AR1xAR1 residual model
  # Needs asreml package (not on CRAN)
  require(asreml)
  dat <- dat[order(dat$xf, dat$yf), ]
  m3 <- asreml(yield ~ gen + rate + nitro + regulator +
                 gen:rate + gen:nitro + gen:regulator +
                   rate:nitro + rate:regulator +
                     nitro:regulator + yf, data=dat,
               rcov = ~ ar1(xf):ar1(yf))
  anova(m3) # Strongly significant gen, rate, regulator
# }
# NOT RUN {
# }