It's a lot more than that. Soil chemistry will teach you where to look for viable grow sites and what kinds of inputs to add as you go to keep the yields abundant. Ag/chemistry will also teach you about nitrogen fixing plants like legumes and how to crop cycle effectively (if you are monocropping which has its own downsides). Ag will teach you about how climate affects what you can plant and for what times of the year they will be worth growing. Genetics will teach you how to acclimatize non native plants over multiple generations of selective breeding. This is barely touching the surface of the knowledge that can empower you in an off grid setting regarding food production from plants and trees.