I've been reading Sustaining Life: How Human Health Depends on Biodiversity.
This is not my usual fare, edited as it is by a couple of M.D.'s and very anthropocentric. But hey, it's a pretty good book - coffee tablish, but very well-crafted essays, including two relating specifically to the food system.
In the chapter on "GM Foods and Organic Farming" they quote Virgil on green manures and no-till methods:
in Part I of "The Georgics"
Sow in the golden grain where previously
You raised a crop of beans that gaily shook
Within their pods, or a tiny brood of vetch,
Or the slender stems and rustling undergrowth
Of bitter lupine...
Thus will the land find rest in its change of crop,
And earth left unplowed show you gratitude.