I would agree with this, even though I have fertilizer, I dont use it. Maybe there should be some like universal fertilizer, where you combine all three (potash and saltpeter could be interchangeable), and when crafted with a soil, makes it a better tier. For example, low fert dirt + uni fertilizer = med fert dirt. You could scale this up by making the amount of the uni fertilizer in the recipe to the tier it would be. So like barren dirt + 3 uni fertilizer = rich dirt. With Terra Preta, the recipes could stay the same with the difference that the uni fertilizer would replace the bonemeal and compost. (Also, obv the uni fertilizer could fertilize dirt with all three types of nutrients)