How do I get the best out of my orange tree?

Does anyone know the best way and time to prune and fertilize an orange tree? I'm no gardening expert but over the past couple of years I have had up to 150 juicy oranges on my one and only tree, which is now four years old. However, this year I had only about 30 smaller ones,  and the few I could eat  were nothing like as good. I did put down some fertilizer several months ago but now the leaves are turning yellow so something is obviously wrong. 

Hi,

The following link is for growing orange trees in the UK but the basics are there for you to adapt to the Spanish climate. After reading through the article it could be that they have had too much water to turn the leaves yellow. Has it rained much this year where you are?

http://www.fruitexpert.co.uk/can-i-save-orange-tree.html

When I clicked on the link for this thread it stated the last post was by Morerosado............................so where is it????

PM sent, Karen.