Effect of Ozone, SO2 and Drought on Soybean Yield
In a completely randomized design with a 2x3x5 factorial treatment structure, researchers randomly assigned one of 30 treatment combinations to open-topped growing chambers, in which two soybean cultivars were planted. The responses for each chamber were the yields of the two types of soybean.
case1402
A data frame with 30 observations on the following 5 variables.
Stressa factor indicating treatment, with two levels
"Well-watered" and "Stressed"
SO2a quantitative treatment with three levels 0, 0.02 and 0.06
O3a quantitative treatment with five levels 0.02, 0.05, 0.07, 0.08 and 0.10
Forrestthe yield of the Forrest cultivar of soybean (in kg/ha)
Williamthe yield of the Williams cultivar of soybean (in kg/ha)
Ramsey, F.L. and Schafer, D.W. (2002). The Statistical Sleuth: A Course in Methods of Data Analysis (2nd ed), Duxbury.
Heggestad, H.E. and Lesser, V.M. (1990). Effects of Chronic Doses of Sulfur Dioxide, Ozone, and Drought on Yields and Growth of Soybeans Under Field Conditions, Journal of Environmental Quality 19: 488–495.
str(case1402) plot(Forrest ~ O3, case1402, log="y", pch=ifelse(Stress=="Stressed",19,21)) plot(Forrest ~ SO2, case1402, log="y", pch=ifelse(Stress=="Stressed",19,21)) fitbig <- lm(log(Forrest) ~ O3*SO2*Stress, case1402) # Residual plot does not indicate any problem. plot(fitbig) # The 3-factor interaction is not statistically significant. anova(fitbig) # Drop the three-factor interaction fit2 <- update(fitbig, ~ . - O3:SO2:Stress) anova(fit2) fitadditive <- lm(log(Forrest) ~ O3 + SO2 + Stress, case1402) summary(fitadditive)
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