Q.Japanese maple
I have a two year old Japanese maple. Last spring the tree fully budded and produced a full leaf bloom. This year, only half the tree has leaves. I have not given up hope that those branches will bud because they are not dead. Is there anything I can give the tree to help it bud? Is there a deficiency that would cause this?

If the tree is still leafless several weeks into spring, it has likely died.
Since you have some leafing branches, check below the bark by scratching the bark.
If it is green there is still life, if it appears tan.
If the branches are still alive it may be that a late frost killed the buds.
In this case the tree should leaf out next year.
https://www.gardeningknowhow.com/ornamental/trees/japanese-maple/japanese-maple-care.htm
https://www.gardeningknowhow.com/ornamental/trees/tgen/tree-scratch-test.htm