Refer to Exercise 14.77 and the study to determine the effects of acid rain on the acidity of soils in a natural ecosystem. Recall that experimental plots were irrigated with acid rain at two pH levels: 3.7 and 4.5. The acidity of the soil was then measured at three different depths: 0–15, 15–30, and 30–46 centimeters. Tests were conducted during three different time periods. The resulting soil pH values are reproduced in the next table. The main objective of the experiment was to compare the acidity of soil irrigated with pH 4.5 acid rain to the acidity of soil irrigated with pH 3.7 acid rain.

a. Use a nonparametric test to compare the soil pH values of the two treatments on April 3.

b. Use a nonparametric test to compare the soil pH values of the two treatments on June 16.

c. Use a nonparametric test to compare the soil pH values of the two treatments on June 30.

d. Comment on the validity of the tests in parts a–c.

Data from Exercise 14.77

Acid rain is considered by some environmentalists to be the nation’s most serious environmental problem. It is formed by the combination of water vapor in clouds with nitrogen oxide and sulfuric dioxide emissions from the burning of coal, oil, and natural gas. The acidity of rain in central and northern Florida consistently ranges from 4.5 to 5 on the pH scale, a decidedly acid condition. To determine the effects of acid rain on the acidity of soils in a natural ecosystem, engineers at the University of Florida’s Institute of Food and Agricultural Sciences irrigated experimental plots near Gainesville, Florida, with acid rain at two pH levels, 3.7 and 4.5. The acidity of the soil was then measured at three different depths, 0–15, 15–30, and 30–46 centimeters. Tests were conducted during three different time periods. The resulting soil pH values are shown in the table above. Treat the experiment as a 2 × 3 factorial laid out in three blocks, where the factors are acid rain at two pH levels and soil depth at three levels, and the blocks are the three time periods.

Transcribed Image Text:

ACIDRAIN April 3 Acid Rain pH Acid Rain pH Acid Rain pH June 16 June 30 3.7 4.5 3.7 4.5 3.7 4.5 0-15 cm 5.33 5.33 5.47 5.47 5.20 5.13 Soil Depth 15-30 cm 5.27 5.03 5.50 5.53 5.33 5.20 30-46 cm 5.37 5.40 5.80 5.60 5.33 5.17