flow an insignificant factor compared with the moisture needs of
crops. But conventional agriculture focuses on maximized yields
through high plant densities. Capillarity is too slow to support
dense crop stands where numerous root systems are competing, but
when a single plant can, without any competition, occupy a large
enough area, moisture replacement by capillarity becomes
significant.

How Plants Obtain Water

Most gardeners know that plants acquire water and minerals through
their root systems, and leave it at that. But the process is not
quite that simple. The actively growing, tender root tips and almost
microscopic root hairs close to the tip absorb most of the plant's
moisture as they occupy new territory. As the root continues to
extend, parts behind the tip cease to be effective because, as soil
particles in direct contact with these tips and hairs dry out, the
older roots thicken and develop a bark, while most of the absorbent
hairs slough off. This rotation from being actively foraging tissue
to becoming more passive conductive and supportive tissue is
probably a survival adaptation, because the slow capillary movement
of soil moisture fails to replace what the plant used as fast as the
plant might like. The plant is far better off to aggressively seek
new water in unoccupied soil than to wait for the soil its roots
already occupy to be recharged.

A simple bit of old research magnificently illustrated the
significance of this. A scientist named Dittmer observed in 1937
that a single potted ryegrass plant allocated only 1 cubic foot of
soil to grow in made about 3 miles of new roots and root hairs every