agridat (version 1.5)

mercer.wheat: Mercer and Hall's uniformity trial of wheat in 1910

Description

Uniformity trial of wheat in 1910

Usage

data(mercer.wheat)

source

Mercer, WB and Hall, AD, 1911. The experimental error of field trials The Journal of Agricultural Science, 4, 107-132. Table 5.

Details

The wheat crop was grown in 1910 at Rothamsted Experiment Station (Harpenden, Herts, England). In one field, a seemingly uniform area of 1 acre was harvested in separate plots, each 1/500th acre in size. The grain and straw from each plot was weighed separately. Row 1 is the south edge, row 20 is the north. Column 1 is the west edge. The dimensions of each plot were approximately 3.2 meters by 2.5 meters.

References

The 'spdep' package includes the grain yields (only) and spatial positions of plot centres in its example dataset 'wheat'.

Examples

dat <- mercer.wheat

require('lattice')
desplot(grain ~ col*row, dat)

densityplot(~grain, data=dat)

xyplot(straw ~ grain, data=dat, type=c('p','r'), main="mercer.wheat - regression")

# require(hexbin)
# hexbinplot(straw ~ grain, data=dat)

require(gstat)
plot.wid <- 2.5
plot.len <- 3.2
nr <- length(unique(dat$row))
nc <- length(unique(dat$col))

xy <- expand.grid(x = seq(plot.wid/2, by=plot.wid, length=nc),
y = seq(plot.len/2, by=plot.len, length=nr))
dat.sp <- dat
coordinates(dat.sp) <- xy

# heatmap
spplot(dat.sp, zcol = "grain", cuts=8,
       cex = 1.6,
       col.regions =  bpy.colors(8),
       main = "Grain yield", key.space = "right")

# variogram
vg <- variogram(grain ~ 1, dat.sp, cutoff = plot.wid * 10, width = plot.wid)
plot(vg, plot.numbers = TRUE)