A quick idea.
Inspired by hugelkultur. Where you have place wood together with the plants. I wonder if you can enhance the water retention ability by drilling holes in the wood. Thereby getting more water to wood surface area.
Then to combat desertification I wonder if you can replace water soaked wood pieces in the soil ever so often. Similiar to putting a seed in the ground. Like drip irregation but using water soaked wood instead.
Maybe a machine can be constructed to perform this task much faster.