2.1 A field experiment to investigate the effect of four levels of nitrogen fertilizer on the yield of three varieties of oats was laid out in a split plot design (Yates, 1937). The experiment comprised six blocks of land, each divided into three main plots. Each main plot was sown with a single variety of oats. Each variety was sown on one main plot within each block: within the block, the allocation of varieties to main plots was randomized.

Each main plot was divided into four sub-plots. A different level of nitrogen fertilizer was applied to each of the four sub-plots within each main plot: within the main plot, the allocation of fertilizer levels to sub-plots was randomized. The results obtained are presented in Table 2.4.