moisture. But if the cracks are filled with dust by surface
cultivation, even this soil type ceases to lose water.

Soil functions as our bank account, holding available water in
storage. In our climate soil is inevitably charged to capacity by
winter rains, and then all summer growing plants make heavy
withdrawals. But hot sun and wind working directly on soil don't
remove much water; that is caused by hot sun and wind working on
plant leaves, making them transpire moisture drawn from the earth
through their root systems. Plants desiccate soil to the ultimate
depth and lateral extent of their rooting ability, and then some.
The size of vegetable root systems is greater than most gardeners
would think. The amount of moisture potentially available to sustain
vegetable growth is also greater than most gardeners think.

Rain and irrigation are not the only ways to replace soil moisture.
If the soil body is deep, water will gradually come up from below
the root zone by capillarity. Capillarity works by the very same
force of adhesion that makes moisture stick to a soil particle. A
column of water in a vertical tube (like a thin straw) adheres to
the tube's inner surfaces. This adhesion tends to lift the edges of
the column of water. As the tube's diameter becomes smaller the
amount of lift becomes greater. Soil particles form interconnected
pores that allow an inefficient capillary flow, recharging dry soil
above. However, the drier soil becomes, the less effective capillary
flow becomes. _That is why a thoroughly desiccated surface layer
only a few inches thick acts as a powerful mulch._

Industrial farming and modern gardening tend to discount the
replacement of surface moisture by capillarity, considering this