Good post Tom. N will increase as an issue because there is a short-term payoff in terms of reduced greenhouse warming to controlling N2O releases (unlike CO2 where the greenhouse payoff of controlling emissions is likely beyond generational or political timescales).

soilcarboncoalition.org

Ironically, fertilizer needed to feed the world is made with fossil fuel.  By the way, nitrogen makes up over 78% of the air, so it is hard to believe that adding more nitrogen to the atmosphere would be that harmful.

From Wikipedia:

Nitrogen fertilizer is often synthesized using the Haber-Bosch process, which produces ammonia. This ammonia is applied directly to the soil or used to produce other compounds...The production of ammonia currently consumes about 5% of global natural gas consumption, which is somewhat under 2% of world energy production.  Natural gas is overwhelmingly used for the production of ammonia, but other energy sources, together with a hydrogen source, can be used for the production of nitrogen compounds suitable for fertilizers. The cost of natural gas makes up about 90% of the cost of producing ammonia. The price increases in natural gas in the past decade, among other factors such as increasing demand, have contributed to an increase in fertilizer price."

Biodigestion not only takes care of the methane released by manure and fertilizer run off (organic fertilizer a byproduct of biodigestion, tends not to run off, as chemical fertilizer does), but also the nitrogen.  296 times the GHG effect of CO2.

Methane is 21 times CO2.  This idea that if 5% of our energy came from biogas from waste, that would offset the whole human CO2 production, seems to be fulfilling itself.

Now exactly how much nitrogen comes from manure and fertilizer run off?  that's a big potential offset boost!  296.

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"...up to about two-thirds of this amount may be offset by the increase in N2O emissions."

So two-thirds of the CO2 taken out of the atmosphere by a chemical ag crop like corn is cancelled by increased nitrogen emitted from the fertilizer.

That leaves only 1/3 of the CO2 released by burning the corn as ethanol, effectively reabsorbed by the corn.  2/3 of corn ethanol's (falsely claimed) carbon neutrality is gone due to ammonia fertilizer.

Look at that huge release of N over the whole of chemical ag.  Equal to 2/3 of the CO2 absorbed in photosynthesis on that crop land.

This makes biodigestion and organic ag an even more effective GHG climate cure.  As good, on the positive GHG canceling side as chemical ag is bad for the GHG balance.

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Nitrous oxide, not nitrogen.  Whoops.  A slip of the keyboard.  But what about the offset from biodigestion?  And substituting organic fertilizer for nitrous oxide emitting fertilizer?

I'm trying to see a flaw in this analysis, but can't.

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In the article, but should have specified which forms of reactive nitrogen are the culprits.

Biogas may save the climate.

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Digestion certainly saves the energy used to make artificial fertilizer. But the residue from biogas, like artificial nitrogen fertilizers lacks fiber or anything to make it stay in the soil. It is liquid or sludge. So most of the nitrogen ends up in the water table for future release.  Biogas has a good energy balance. (It takes very little energy to convert the right balance of organic material to gas, because bacteria do most of the work.)But if you are concentrating on the nitrogen balance from producing it, you end up with more NxOx in the atmosphere than you would with aerobic composting.

...would help with nitrogen, to some extent, since some of the sources for human-related nitrogen releases are also responsible for C02 production.

Well Gar, currently here in Wisconsin farmers use wood chips for bedding for cows.  The whole mess goes in the digestor, gas is produced, but the chips are softened, not totally digested.  They go back, after a rinse and dry to the cows, a softer gentler bed.

So fiber could be partially digested then returned to the soil as an organic fertilizer soaked soil amendment.

Why does run off occur with chemical fertilizer?  Because the soil is essentialy an inert hydroponic growing media.  To get good results in hydroponics, flooding with hutrients must happen frequently.  The excess running off into the drainage system.

The gentle nurturing nature of organic soil amendment in restoring the soil ecosystem makes the soil fertilize itself.  It is no longer inert as in agrichem hydroponic farming.  The nitrogen stays put in the bacterial community.  Locked into the living organic matter.

We all know as gardeners that green manure, like fresh grass or weeds, or manure itself emits a lot of ammonia when first put on the compost pile, after a hot period it smells fresh and earthy even as aerobic composting continues.

That first phase was the wet manure and green material breaking down in aneroebic digestion.  That emits methane.  If that first phase is done in a digestor the methane and nitrous oxide is entrapped  and can be defused of it's GHG extreme properties.

After a few weeks the organic soil amendment can be put in the soil and it will no longer emit large quantities of gas.  Instead it will break down slowly, mainly emitting cO2.  A fraction as bad a GHG as methane.

This new revelation about nitrous oxide is quite a boost for biodigestion and organic farming.

http://amazngdrx.blogharbor.com/blog

Imagine those rice fields that emit so much methane and nitrous oxide powering biodigestors.  Along with some manure the rice straw is a huge clean energy and GHG savings source.

The organic soil amendment substituted for the chemical fertilizer would help the soil store carbon year after year, as thick as peat bogs or prairie soil.

Look to the farms.  To solve the climate crisis, farms with plenty of wind farms on them.  And literally gigatons of carbon sequestration and titanic GHG cancellation.

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