Fertilizer Use on Orange Tree

[Jaxinspain]

I have a bag of Compo Nitrophoska Azul Especial fertilizer which I plan to use on a small orange tree I'm planting tomorrow. Does anyone know how much I should use as I can't make head or tail of the instructions? I've been on their website but that wasn't much use either. I don't want to over feed it in case it does any harm to the tree. I didn't buy it myself so couldn't ask at the Garden Centre at the time.

Many thanks
Jackie