Carbon Debt, Bio Fuel and Food Grain shortage

Are you surprised how these are related? As conventional fuel is getting more and more expensive, government is trying on alternatives like Bio fuel at the cost of regular farmland(more monies). Now the question is where to make these bio fuels. Bio Fuels can be made from waste products, or grown on abandoned lands or normal lands. It is beneficial if it is done from first two sources. Most bio fuels may increase green house emissions (in the form of carbon dioxide) because clearing grassland or forests to plant them releases Carbon Dioxide. Trapped Carbon is released into the atmosphere when vegetation burns or decays as land cleared. so, this carbon debt make more damage than economies gain by using biofuels in place of fossil fuels. Now think about impact of bio fuels on environment and damage compare to gain by them when we want to replace or substitute fossil fuels or regular petroleum products?