Earlier quoted context omitted.
Wood is mostly cellulose (which is all carbon, hydrogen, and oxygen). There's some calcium and potassium, but not that much. You are correct that it's not entirely renewable.
Not sure what you mean by renewable? Would carbon, hydrogen and oxygen be more renewable than calcium and potassium? They are all just elements we have a lot of on earth. And those elements don't get used up. Toss your wood on a compost pile, and you can re-use them?
Leibig's Law of the Minimum states that it is the specific nutrient which is limiting of growth or metabolism which is most crucial. This is a point missed in numerous dicussions of growth or limits. Typically this is a fairly major nutrient such as nitrogen (fixed from the atmosphere, but at high metabolic cost, largely through microbes which are sybmiotes with legumes). Phosphorus and potash are the other most heavily utilised, and most frequently limiting nutrients. In parts of Australia, a land that is remarkably inactive, tectonically, critical micronutrients arrive as wind-blown dust, much from India or volcanic eruptions in Indonesia. A few grams per hectare can make a significant difference in crop yields.
Soil alkalinity is another major factor, as is drainage charcteristics, with sandy, clay, or high-carbon soils all being favoured or unsuited to specific plants. Then of course, climate, temperature, and precipitation.