In 2009, a programme from BBC's 'The Natural World' series covered this precise issue: http://www.bbc.co.uk/programmes/b00hs8zp

The programme's presenter is a farmer, from a family of farmers. She explored the latest developments in 'sustainable' agriculture and arrived at some surprising conclusions. 'Permaculture' was one of the most radical ideas, and the suggestion is that it could truly revolutionize modern farming.

It was a thoughtful, reasoned and compelling commentary; a programme which I found important enough to make an 'offline' copy for myself...