The article referred to in Exercise 1 also considered the effect of gypsum on the electric conductivity (in dS m−1)

of soil. Two types of soil were each treated with three different amounts of gypsum, with two replicates for each soil–gypsum combination. The data are presented in the following table.

Soil Type Gypsum (g/kg) las Animas Madera 0.00 1.52 1.05 1.01 0.92 0.27 1.49 0.91 1.12 0.92 0.46 0.99 0.92 0.88 0.92

a. Is there convincing evidence of an interaction between the amount of gypsum and soil type?

b. Can you conclude that the conductivity differs among the soil types?

c. Can you conclude that the conductivity differs with the amount of gypsum added?