An experiment was conducted in Iowa in 1944 to see how different varieties of alfalfa responded to the last cutting day of the previous year (Snedecor and Cochran 1967). We know that in the fall alfalfa can either continue to grow, or stop growing and store resources belowground in roots for growth during the following year. Thus, we might expect that later cutting dates inhibits growth for the following year. On the other hand, if plants are cut after they have gone into senescence, there should be little effect on productivity during the following year. There are two factors: 1) variety of alfalfa (three varieties were planted in each of three randomly chosen whole plots), and 2) the date of last cutting (Sept 1, Sept. 20, or Oct. 7). The dates were randomly chosen split plots within the whole plots. Replication was accomplished using six blocks of fields.
data(alfalfa.split.plot)The dataframe contains four variables:
yieldAlfalfa yield (tons per acre).
varietyAlfalfa variety. A factor with three levels "L"= Ladak, "C" = Cosack, and "R" = Ranger describing the variety of alfalfa seed used.
cut.timeTime of last cutting. A factor with three levels: "None" = field not cut, "S1" = Sept 1, "S20" = Sept. 20, or "O7" = Oct. 7.
blockThe block (whole plot replicate). A factor with six levels: "1", "2", "3", "4", "5", and "6".