In the split-plot design shown here, the treatments are three varieties of oats (Victory, Golden rain and Marvellous) and four levels of nitrogen (0, 0.2, 0.4 and 0.6 cwt). As it is feasible to work with smaller plots for fertiliser than for varieties, the six blocks were initially split into three whole-plots and then each whole-plot was split into four subplots. The varieties were allocated (at random) to the whole-plots within each block, and the nitrogen levels (at random) to the subplots within each whole-plot. In a randomized-block design, we have a hierarchical structure with blocks and then plots within blocks.