Drill two rows of holes, each row being about 25° off the top centerline of the pipe. Space the holes about 4 per square side. use a No 60 drill bit so that the nozzles are 0.040″ holes (1 mm for you metric folks.).
The beauty of this system is that it automatically meters about 4 cups of water per square. So it will likely dedicate one bucket per 4×4 box. Dumping one bucket of water into the irrigation bucket is certainly faster than fighting your way through the plants to ladle water onto 16 separate squares.