Small-scale method
This method is very small scale, irrigating a single tree (I saw it for pomegranites in Iran), but appears effective and requires only pottery as a technology base.
Make a spherical pot, roughly 40 cm diameter with thick walls (about 5 cm) to withstand roots seeking water and a long (30 cm) narrow tubular neck. Glaze most of it but leave a large circular area on one side unglazed. Bury it with only a bit of neck exposed next to your tree with the unglazed part toward the tree. Fill with water and cover the opening; top up as needed. The water seeps out slowly toward the tree and, since it is not on the surface, evaporation loss is almost zero.
The pots may survive mild frost because they are mostly undergound, but this would probably not work in a really cold area. Pashley (talk) 08:44, 25 June 2014 (PDT)