Bottom line: Just because lots of governments decide some path is a good idea doesn't mean they all aren't being stupid.

That's Randall's conclusion about the world wide rush to biofuel production though there are arguments that doing so produces more GHGs than equivalent fossil fuels would produce. The nub of the argument in this case is denitrification - the microbial breakdown of nitrates applied to crop lands. In doing so these soil bacteria emit nitrous oxides and other gases, and the N₂O is a more potent greenhouse gas than CO₂.

Nitrous oxide (N₂O) is a clear, colorless gas, with a slightly sweet odor. Due to its long atmospheric lifetime (approximately 120 years) and heat trapping effects —about 310 times more powerful than carbon dioxide on a per molecule basis — N₂O is an important greenhouse gas.

Nitrous oxide has both natural and human-related sources, and is removed from the atmosphere mainly by photolysis (i.e., breakdown by sunlight) in the stratosphere. In the United States, the main human-related sources of N₂O are agricultural soil management, mobile and stationary combustion of fossil fuel, adipic acid production, and nitric acid production. N₂O is also produced naturally from a wide variety of biological sources in soil and water. On a global basis, it is estimated that natural sources account for over 60% of the total N₂O emissions (IPCC, 2001c). . .

Global average atmospheric concentrations of N₂O have increased from about 270 parts per billion by volume (ppbv) in 1750 to 314 ppbv in 1998, which equates to a 16% increase for the period. In the last two decades, atmospheric concentrations of N₂O continue to increase at a rate of 0.25% per year. There has been significant multi-year variance in the observed growth of N₂O concentrations, and the reasons for these trends are not yet fully understood. . .

The cited articles seem to do some hand waving and make many assumptions. It's not clear to me whether they have a legitimate criticism of biofuels since the things they complain about are true of agriculture and natural systems in general as well as many civilized behaviors such as waste water treatment and burning fossil fuels. Another way to see the issue is that these behaviors should be modified to explicitly reduce N₂O production as part of our general concern about GHGs. It isn't a biofuel issue so much as an agronomic issue. Biofuels are stupid, but perhaps not for this reason.

All is not lost. Even though this is not a red flag climate issue it does give us an excuse to neep about redox potential.

Denitrification proceeds through some combination of the following steps:

nitrate -> nitrite -> nitric oxide -> nitrous oxide -> dinitrogen gas

Or expressed as a redox reaction:

2NO₃- + 10e- + 12H+ -> N₂ + 6H₂O

There's an interesting symmetry that those of you who have been singing along may appreciate.

Much biological energy is stored and released by means of redox reactions. Photosynthesis involves the reduction of carbon dioxide into sugars and the oxidation of water into molecular oxygen. The reverse reaction, respiration, oxidizes sugars to produce carbon dioxide and water.

Both plants and animals respire, but photosynthesis - the protagonist in the previous post - is a special skill performed mostly by plants. Plants need nitrogen as much as they need carbon, water and sunlight. The nitrogen cycle will occur whether we like it or not. Cousins of the bacteria that do denitrification do nitrification. Yin and yang so to speak. It seems to me that the wisest thing we can do is to seek balance in our agronomic interventions, and so get more vegetation for our efforts with less N₂O, and focus in other areas for GHG reduction. We are likely to get more benefit from reducing the N₂O output from fossil fuel burning, waste water treatment and similar industrial and urban activities.