As a neophyte, I'm guessing the point is to allow the nutrient minerals/elements to dissolve but far more slowly so that if e.g. there is sharp rainfall after a

As a neophyte, I'm guessing the point is to allow the nutrient minerals/elements to dissolve but far more slowly so that if e.g. there is sharp rainfall after application it's not all lost. The paper says complete solubility took 6 days or more, which is persisting. If the stuff is bioavailable but less prone to migration it's a massive upside: less applied for more benefit and less runoff contamination. Making glasses does mean changing the fertiliser manufacturing process. I wonder if NPK mixes can be post processed? And what's the extra energy burdens?