The nitrogen will leach out with rain, at least after it is converted to nitrate form. Phosphate and potash don't leach out with rain but can be tied up by the soil and thus become unavailable to the tree. So nitrogen needs to be applied once or twice a year if needed. P and K only need be applied when a soil test shows they are lacking. Applying too much of any nutrient is wasteful, bad for the environment, potentially problematic by affecting uptake of other nutrients, and in the case of nitrogen can reduce fruit eating quality. Go easy on the fertilizer, especially something like 10-10-10. Fruit trees usually need more N than P or K.

Don't the professionals use a liquid form of fertilizer? I try to go very light on fertilizer applications, except in container grown plants..

"Don't the professionals use a liquid form of fertilizer?"

An advantage of foliar fertilizer is that sometimes the roots won't pull some nutrients out of the soil (for instance when the soil is saturated with water) and are very fast acting. They can also be useful to counteract fruit disorders like bitter pit in apple. Foliar fertilizers can also be applied easily, being generally tank mixed with pesticides that would be applied anyway.

Foliar fertilizers are more expensive than soil applied products so their use is really only justified when there are no other options.

i have sandy well drained soil with adequate amounts naturally of P and K. I have learned that for best results in my soil I need to apply the max recommended amount of nitrogen twice annually. I use urea which is cheap and 40% nitrogen.

wow.... What do you mean by "Best results" in the context of FRUIT trees?

I personally found that fruit quality (defined as Brix and Flavor) is miserable when the fruit trees get a bunch of Nitrogen fertilizer....

Minerals may be a different situation... but if you want tasty fruit - you don't drop much if any N....

Thanks