Author: Kevin Wright
Date: 2026-08-07

# Plotting field maps with the desplot package

#### Kevin Wright

#### 2026-08-07

# Abstract

This short note shows how to plot a field map from an agricultural experiment and why that may be useful.

# R setup

    library("knitr")
    knitr::opts_chunk$set(fig.align="center", fig.width=6, fig.height=6)
    options(width=90)

## Example 1

First, a plot of the experimental design of the oats data from Yates (1935).

    library(agridat)
    library(desplot)
    data(yates.oats)
    desplot(yates.oats, block ~ col+row,
            col=nitro, text=gen, cex=1, out1=block,
            out2=gen, out2.gpar=list(col = "gray50", lwd = 1, lty = 1))

## Example 2

This next example is from Ryder (1981). Fit an ordinary RCB model with fixed effects for `block` and `genotype`. Plot a heatmap of the residuals.

    library(agridat)
    library(desplot)
    data(ryder.groundnut)
    gnut <- ryder.groundnut
    m1 <- lm(dry ~ block + gen, gnut) # Standard RCB model
    gnut$res <- resid(m1)
    desplot(gnut, res ~ col + row, text=gen, cex=1,
            main="ryder.groundnut residuals from RCB model")

Note the largest positive/negative residuals are adjacent to each other, perhaps caused by the original data values being swapped. Checking with experiment investigators (managers, data collectors, etc.) is recommended.

# Infrequently asked questions

## How do I change the ordering of panels?

Make sure that the panel variable is a factor and then change the levels of the factor.

In the example below, the first three panels are set to the levels C1, C3, C5. The other levels remain in the same (relative) order.

    library(agridat)
    library(desplot)
    data(besag.met)
    desplot(besag.met, yield~col*row|county, main="default county ordering")
    library(forcats)
    besag.met <- transform(besag.met,
                           county=fct_relevel(county, c("C1","C3","C5")))
    desplot(besag.met, yield~col*row|county, main="custom county ordering")

## References

Ryder, K. 1981. “Field Plans: Why the Biometrician Finds Them Useful.” Experimental Agriculture 17: 243–56. https://doi.org/10.1017/S0014479700011601.
Yates, Frank. 1935. “Complex Experiments.” Journal of the Royal Statistical Society Suppl 2: 181–247. https://doi.org/10.2307/2983638.