Biodegradable veins--the tubes could also come in various chemical flavours such that if you had a certain soil problem X you choose tube type Y which, when it biodegrades (in a year? two?) releases relevant chemicals into the soil to bring it back to maximum health--
I really like this idea! Sorry Asinus Asinum Fricat, I went a bit OT. Don't fight forces, use them R. Buckminster Fuller.