Mr Gardener wrote:
.... When water is below the surface, gravity no longer
determines the direction of flow, and the water disperses
horizontally, by capillary action, I think, wetting an area about a
foot to two feet on either side of the hose....


Not quite. While capillary action disperses the water better from a
buried hose, gravity acts on it all the same. The advantage to a buried
hose is that the water can go up as well as out. However, if you try
this in pure sand, you fill find the moisture goes predominantly
downward. The extent to which the moisture will spread depends strongly
on the type of soil you are using.

On the subject of soil type, I ran across a simple test to find your
soil's place on the old soil triangle.
http://everything2.com/?node_id=1698166