A white paper I wrote (along with my colleagues Tim Boucher and Samantha Atwood) is now available at:
http://www.nature.org/science-in-action/science-features/measuring-sustainability-in-agriculture-focusing-on-outcomes.xml
The basic premise is that the measure whether or not agriculture is truly sustainable we absorb to get past just measuring practices (what we attain,such as conservation tillage or riparian buffers) and walk to measuring outcomes (water quality & quantity, soil quality, and etc.). We review the literature and suggest several metrics for environmental variables,although we attain not include agronomic variables such as yield which are portion of overall sustainability.
Source: blogspot.com