Thanks! I did a little bit more reading on the subject. It seems like P and K are the two main minerals provided by fertilizer, but there's also zinc, copper, iron, manganese, and, oddly, molybdenum. And some plants apparently also deplete other elements, like sugar beets use a lot of boron.

I wonder about the environmental tradeoffs between using crop rotation vs. fertilizer for some of the micronutrients. On the one hand, there's an environmental cost to creating fertilizer, there's dangers of over-fertilizing, runoff, etc. But a crop rotation system means some fields will have to lie barren, or with less valuable crops, and potentially with lower yields, which means you need more farmland to grow the same amount of food, which means clearing more forests. Of course, I'm not even a novice in this subject, I'm sure there's a lot I'm missing.

The rotation/organic/etc argument is that properly managed soil & fields sustain their yields indefinitely with significantly less fertilizer, water, etc input, whereas the traditional industrial ag model achieves higher yields initially but the soil quality & yields decline rapidly & require ever more fertilizer, water, etc input. In short, the first model has lower peak yields but is more sustainable; the second has higher peak yields but "uses up" the land, and within only 1-3 decades at that.

A related example of the consequences of "using up" land can be seen with bananas. In that case, a deadly banana fungus is slowly, inexorably spread through the soil by human activity. Eventually a plot of land becomes unusable for growing bananas due to the spread of the fungus. No matter, the banana company just cuts down more rainforest for new land and abandons the old plot. Later, in perhaps ten years, the new plot will be contaminated & unusable, and the cycle continues.