There is not much source for organic fertilizers in the Philippines compare here in the US.
What u can do imo is that u put any kind of manure (except human waste), wood ash, and mulch away. As time passes by it will break down the organic matter, thus breaking down the clay soil converting them to nutrients. It may take awhile, though it will work in time...
Unless u want a quick reaction, go for synthetic (high in iron, magnesium, sulfur & zinc). But i dont recommend using synthetic fertilizers.
This is just my opinion. U could ask other any other experienced growers here.
