The best practical illustration of what is known as sub-irrigation is found in the raisin-producing district near Fresno, California. No water is applied to the surface. Six feet below the surface is found a nearly water-tight clay deposit with a porous soil above. The water runs in ditches down to the clay and seeps under the vineyard, rising to the roots by capillary attraction.
Another kind of sub-irrigation is found in California, on the bottom lands, on which sugar-beets are grown, in China, and at other points. These lands are in the stream valleys and are sub-irrigated by the seepage water from orange and other irrigation on the higher elevations. The Chinese gardeners also seek such land for vegetable-growing in California, near Phoenix, Arizona, in Colorado, and at other points where the seepage water from higher land sub-irrigates lower-lying land without making swamps or ponds, which often happens.
In Wisconsin, near Sparta, and at other points, sandy lands with clay subsoil are sub irrigated for cranberry-growing. Ditches surround the planted tracts, in which water is introduced from running streams or from reservoirs.
Close observation will disclose hundreds and even thousands of these naturally sub-irrigated tracts in about every State of the Union which have not as yet been utilized for gardening or fruit-growing.