Step 2: Identify the parts of the system and its boundary.
Pollan provided an overvew of what's happening in the soil. To understand more about the “healthy soil" system, read this essay, and think about the parts of the "healthy soil" system that's described.
It helps to imagine an boundary between the parts of the system you want to study and everything else. When you identify the key parts that most directly influence the behavior you’re considering, you're helping to define this boundary. Without the boundary, it’s easy to be overwhelmed or miss the story you are most interested in.
So, to understand about how soil stays healthy or gets depleted, you will be considering the factors that maintain or remove soil nutrients and how humans can affect these. For the time being, you will not be considering other factors such as weather, industrial or government policies, use of chemical fertilizers, or use of pesticides.