Question
If I water and fertilize in a desired dripline quadrant will the root growth be concentrated in that quadrant. Especially if there is a root barrier in the other quadrants. The tree species is Quercus Virginiana. and the problem is keeping the roots out of the septic drainfield as long as possible.  The oak tree is 5" in dia and about 15' tall.  It is growing about 8 feet from the drainfield. the growing space the opposite direction of the drain field is open.

Answer
You can try it but I do not think it will work. Roots tend to grow toward a water and nutrient source and if the septic line is discharging near the tree then the roots will grow that way as fast as toward the fertilized side. The roots tend to grow out in all directions from the trunk so it will be very difficult to "train" them to grow one way. You can add chemical to the septic tanks and lines to stop the roots from entering them and keep the pipes unclogged.