There are at least 19 chemical elements required for plant growth. Each chemical element has one or more specific functions within the plant, which cannot be taken over by another. As the plant grows, the daily demand for nutrients increases. Of the major nutrients, Mg is essential for both plant and animal growth and health, and K and Na are often involved in animal health issues.
It’s an easy concept to think of the soil as a bank. If you remove nutrients in products sold off the farm, then you need to replace them to keep a state of ‘nutrient balance’ in the bank.
You cannot consider fertilisers without knowledge of the soil. The key points will only be touched on here. In geological terms, New Zealand it's a very young country, with major ash storms from volcanos being deposited as recently as 1300AD. NZ Soils have all been surveyed, described, and mapped by what used to be the government's Soil Survey.
One thing is for sure - if you thought the whole business of making money from 'farming carbon' was complicated, you were terribly wrong. It's much more complicated than you could imagine. It's mind boggling to think of the work that went into getting this whole carbon business worked out for New Zealand.