I'd vote for something direct or indirect. I can't think of another way to do it.

Direct would be a probe of some sort that you stick into the ground and pump your fert and water into.

Indirect would be some sort of traditional irrigation. I think the most efficient would be a slow or drip irrigation that would soak into the ground rather than running off.

Any number of ways to accomplish both. PVC appears simple but the bore sounds large. The commercial root feeders have an oversized needle type applicator. Municipalities often put bags that hold I'm guessing 5-10 gallons of water around trees that release the fluid over days I assume. I'm not sure if they can adjust the flow rate or if it is fixed by the bag material. You can easily purchase a drip irrigation system but you have to put up with semi-permanent tubing to the plants.