I did a site search on the USDA.gov website. The search string was "sub-irrigation" OR subirrigation. The following (see below) was the first hit of 284. Note the first sentence "half the amount of water."
Note also the study was conducted in a container nursery (i.e. container garden). The key fact is that the plants were watered by sub-irrigation, just the way you can with DIY sub-irrigated planters (SIPs). See recent posts about "bubble SIPs" here and here, or see the bubble SIP archive.
Know that bubble SIPs are scalable. For larger planters simply increase the size of the "bubble" (i.e. the water/oxygen reservoir). A chart for this is on my to-do list. Information of this type will definitely be in the book I am writing.
This USDA information was not meant for your eyes as a gardener or consumer. It was meant to be read by growers (i.e. farmers).
Now let's do the same site search on this website (it also "belongs" to the USDA via their extension program). It is meant to serve gardeners, consumers, educators, school children...and you.
The same sub-irrigation site search produces 0 results! There is nothing on the "master gardener" site about water-conserving sub-irrigation at this critical time of a drought crisis.
As a consumer, or gardener or taxpayer, how do you feel about this? Someone is not talking straight...at our expense!
With about half the amount of water, subirrigated Metrosideros polymorpha Gaud. (Myrtaceae) grown 9 mo in a greenhouse were similar to those irrigated with an existing fixed overhead irrigation system; moss growth was about 3X greater in the fixed overhead system after 3 mo. Moss growth was affected by the rate of preplant controlled release fertilizer added (more fertilizer, less moss) and moss maturity, quantified as presence or absence of sporangia, was slowed with subirrigation. About 5 g nitrogen (N) leached per m2 (0.02 oz/ft2) of greenhouse bench under the fixed irrigation system, whereas none was lost from subirrigation. Besides Metrosideros macropus, the USDA Forest Service and Purdue University are evaluating subirrigation for nursery production of other species. To date, the results indicate subirrigation may be a useful technique for growing native plants with large canopies where conventional irrigation systems are less effective, or where water use or other environmental concerns are paramount. Dumroese RK, Pinto JR, Jacobs DF, Davis AS, Horiuchi B. 2006. Subirrigation reduces water use, nitrogen loss, and moss growth in a container nursery.