Suppose that the 60 soybean plants were actually two different varieties: 30 Chemgro soybean plants and 30 Pioneer soybean plants and that the two varieties have different yields. Design an experiment that could be used to measure the effect of level of fertilizer while taking into account the variety of soybean.

Approach Because the yields of the two varieties may differ, use a randomized block design, blocking by variety, to determine which level of fertilizer results in the highest yield.