An experiment was set up to compare the effects of different soil pH and calcium additives on the increase in trunk diameters for orange trees. Elemental sulfur, gypsum, soda ash, and other ingredients were applied annually to provide pH value levels of 4, 5, 6, and 7. Three levels of a calcium supplement (100, 200, and 300 pounds per acre) were also applied. All factor€“ level combinations of these two variables were used in the experiment. At the end of a 2- year ­period, three diameters were examined at each factor€“ level combination. The data appear next.

a. Construct a profile plot. What do the data suggest?
b. Write an appropriate statistical model.
c. Perform an analysis of variance and identify the experimental design. Use α = .05.

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Calcium pH Value 100 2300 6.3 52 74 5.9 7.0 6.7 6.3 7.66.1 7.1 74 73 74 7.3 75 7.5 7.1 7.2 7.6 7.6 7.2 7.2 7.5 74 7.87.0 72 74 7.5 7.066 7.2 6.9 4.0 n5.0 6.0 7.3 7.0 6.4