permaculture

["Lawrence F. London, Jr." <lfl@intrex.net>]

Double digging a garden plot may be the best way to improve soil without using
any power equipment. Alan Chadwick and John Jeavons developed the method
and popularized it through lectures, workshops and publications. This method
began being widely used during the 1960's-1980's as many companies marketed
imported English-style garden tools that worked best when using this 
gardening method.
The basic array included short D-handled tools such as a digging spade 
(straight point),
a digging fork and a spade fork. You could do it all with these three tools. 
A rake,
garden spade, pitchfork or compost fork and manure fork or potato digger were 
also used.

A few references:

Ecology Action
http://www.growbiointensive.org/biointensive/GROW-BIOINTENSIVE.html
Jeavons' Books, Seeds and More:
http://www.bountifulgardens.org/
John Jeavons' books:
"How To Grow More Vegetables That You Thought Possible On Less Land Than You Can 
Imagine"
New 6th Edition
http://www.growbiointensive.org/biointensive/book.html

Alan Chadwick lectures
http://www.ibiblio.org/ecolandtech/orgfarm/permaculture/Alan.Chadwick/

Gardening Hand Tool SOurcelist
http://market-farming.com/gardening-hand-tools.faq