Sustainable fertilizers do not have to be 100% organic to be sustainable. In fact the 100% organic ones are not usually the best choice.
Most "Organic" fertilizers are derived from and therefore contain animal bi-products as their source of the plant nutrients they provide. These animal bi-products are typically high in salts, heavy metals and animal proteins. Things that plants and the soils they grow in don't like. In addition, they rarely provide a satisfactory plant response compared to synthetic fertilizers.
Further compounding the issue is that the organic plant nutrients they contain come along with the rest of the organic matter in the bag which is again, typically an animal bi-product. There are much better choices of organic matter.
Consider a different approach. One that allows the use of the finest "Plant Derived" organic materials combined with the finest synthetic plant nutrients. An approach that gives the best of both worlds: Excellent, predictable plant and soil response while also being environmentally sustainable and pro-active.
This approach is definately green. Managing our plants in a manner that is more supportive of healthy soils is Green - and not just because your turf and plants will be greener in color. It allows turf and plants to use all nutrients much more efficiently, allowing for a reduction in the amounts of fertilizer required. This is because in healthy soils, the nutrients are assimilated and held in the root zone by the beneficial microbes. This reduces run-off, leaching and evaporation by keeping the nutrients where the plant can use them and keeping them out of the air and ground water where they are not wanted.
It gets greener still. Your now healthier plants (due to healthier soil) are more resistant to diseases and other pests so that fewer fungicides, herbicides and insectides are needed. The beneficial soil micro-organisms also break down toxins and chemical residues in the soil leaving it cleaner and greener.
This approach is more than sustainable, it is regenerative, and actually reverses the damage done by the over-use of typical fertilizers and animal bi-products.