We know that producing fuels from plant material is probably
beneficial from the perspective of carbon dioxide emissions.
After all the plants are absorbing carbon dioxide from the
atmosphere as they grow rather than just releasing carbon that
was trapped in the ground. The overall energy equation is more
problematic at least with current feed-stocks like corn, canola
and soy. Depending on the processes used, it may well take more
energy to grow and process the crops than you get out. As we
move toward cellulosic and algae based feed-stocks, the balance
should improve dramatically.  However, there is another concern
with biofuels. The current crops that are being used require
huge amounts of nitrogen-based fertilizers to produce. It turns
out that a significant portion of the nitrogen in the
fertilizers is actually consumed by bacteria in the ground and
then given off as nitrous oxide. Previous estimates had placed
this at about two percent of the nitrogen, but new studies place
that number closer to three to