The objective of this research was to investigate the long-term effects of irrigation with treated waste water on some chemical soil properties.
The investigation was carried out by comparison of soil properties in two different fields: one irrigated with the effluent from Parkan Waste water Treatment Plant over a period of six years, and the other one irrigated with water over the same period of time. Soil samples were taken from different depths of 0-15, 15-30, 30-60, 60-100 and 100-150 cm in both fields, and analyzed for various chemical properties.
For visual summaries, I am going to plot depths of soil and element (with line and bar plots). However, I also need to fit a linear model with one categorical and one continuous predictor. How can this be done in R?
Thanks for your answer!