A 240-acre field is divided into 24 10-acre plots. The plots are randomly assigned to 12 groups, with the two fields in each group receiving the same treatment of fertilizer and irrigation. Three levels of fertilizer are applied (low, medium, and high), and four levels of water application are used (none, low, medium, and high). The crop yield in bushels per acre is determined at the end of the season.

For the yields shown in the data table opposite, determine

(a) if the interaction between irrigation and fertilizer application is significant;

(b) if the mean crop yield is affected by fertilizer application; and

(c) if the mean crop yield is affected by irrigation rates. Use a 5% level of significance.
Water Application Fertilizer None Low Medium High Low 69 75 81 89 102 106 109 113 Medium 89 95 96 100 107 111 110 116 High 105 113 106 110 99 105 95 99