Question
I have a small garden and would like to develop a rain basin to collect rain water and through field lines, pvc pipe construct a gravity feed system to water beneath soil surface any suggestions

Answer
There are a couple of things I can think of.  You need some increase in pressure to make sure that the water fills all the pipe and then will seep out of the holes.  I would suggest elevating the storage container several feet to help provide gravity pressure to the system.  You will need to have a manifold mainline to supply your header pipe in several locations (instead of one location).  This will equalize pressure in the system.  I would use 3/4" pipe for the rows, drilling them out every so often with a small hole for the water to come out.  You may even attach a small piece of tubing to the hole to help prevent soil from plugging up the piping.  At the end of each row, run a 2' piece of pipe straight up in the air, maybe supported by a stake or something.  This will help equalize pressure in the line so that water will flow more evenly, and not just at the end of the pipe.