We have been planting a lot of trees here in Southwest Texas for the past 5 years (average about 15-18 in rainfall). During which we have been experiencing an intense drought. One method that we use and has had relative success is making a mulch basin or Zai holes. Both methods have yielded excellent results for some species we have planted including peaches, plums, apricots, vitex, live oak, red oak, and more.
If you experiment with burying
wood or other organic matter under your tree remember that it will rob the tree of nutrients (especially nitrogen) for the first 2 or 3 years. You will certainly need some type of drip irrigation to mitigate for the lack of rainfall.
Check out these Deep Drip Tree Watering Stakes. Haven't used them, but it makes a lot of sense. Here is a link:
http://www.sprinklerwarehouse.com/Root-Watering-Devices-s/7848.htm
Pricey, but might be worth the cost. Any moisture near the top of the soil in a harsh desert environment is transpired during the intense summer heat and wind. Thus, if you can get the water deeper from the start by all means do so.
My father use to drill a hole with the PTO driven post hole digger near a pecan seedling. He would insert a 4" PVC with holes drilled in the sides (not too big or dirt will fill in) and back fill it with dirt. He would use this to water and fertilize the trees. Back then PVC was cheap. Not so much anymore.
That's my two cents. Good luck!