A farmer wishes to test the effects of a new fertilizer on her
potato yield. She has four equal-sized plots of land. One plot has
sandy soil, one has rocky soil, one has clay-rich soil, and one
has average soil. She divides each of the four plots into three
equal-sized portions and randomly labels them A, B, and C. The
four A portions of land are treated with her old fertilizer, the
four B portions of land are treated with the new fertilizer, and
the four C portions of land are treated with no fertilizer. At
harvest time, the potato yield is recorded for each section of
land. What is the response variable in this experiment?