In one of the pictures, it looks like the two pvc tubes are connected with a DWV coupling. You really want to use schedule 40 for irrigation. DWV couplings don't have much surface area to mate with your piping and will generally fail under pressure.
For a typical residential scenario, 1 inch PVC works well. 1 inch pvc under modest pressure can carry upwards of 40 GPM. And a typical irrigation head will use around 2 GPM.
When PVC welding, always be sure to use primer first. I've seen PVC welds fail on irrigation tubing when primer is not used. It can take a decade or so, but they can and do fail. Usually, you get lucky and the dirt holds things together.
If you're using schedule 40 PVC, you only need bury a couple of inches below the surface. Schedule 40 resists shovel penetration quite well.