One can check rapidly the well known wikipedia for answers on subject they are not familiar with. Industrials and investors mainly do stuff because they can earn a profit. If something can be done cheaply with a new technology, competitions laws tells us that the lower cost way will win.

That is why most hydrogen, thus amonia, is made using natural gas with the Haber-Bosch process.

Links to the article :
http://en.wikipedia.org/wiki/Haber_process

Exerp from the article :

Ammonia was first manufactured using the Haber process on an industrial scale in 1913 in BASF's Oppau plant in Germany. During World War I, production was shifted from fertilizer to explosives, particularly through the conversion of ammonia into a synthetic form of Chile saltpeter, which could then be changed into other substances for the production of gunpowder and high explosives (the Allies had access to large amounts of Chile saltpeter from natural deposits in South America; Germany had to produce its own). It has been suggested that without this process, Germany would not have fought in the war[6], or would have had to surrender years earlier.

Prior to the use of natural gas as a hydrogen source, electricity was used to electrolyse water. The Vemork 60 MW hydro electric plant in Norway was constructed purely to produce hydrogen via electrolysis of water as a precursor to ammonia production, and up until the second world war provided the majority of Europe's ammonia.

But you can follow the rest of the article wich states that (emphasis added):

Nowadays, the bulk of the hydrogen required is produced from methane (natural gas) using heterogeneous catalysis, because this requires far less external energy input compared to the electrolysis of water. However, the source of the hydrogen makes no difference to the Haber-Bosch process, which is only concerned with synthesizing ammonia from nitrogen and hydrogen

After that, the articles goes on with the science, chemestry, and engigeering part of the process and then, almost at the end, a part on environment and economics :

The Haber process now produces 100 million tons of nitrogen fertilizer per year, mostly in the form of anhydrous ammonia, ammonium nitrate, and urea. 3-5% of world natural gas production is consumed in the Haber process (~1-2% of the world's annual energy supply)[1][13][14][15]. That fertilizer is responsible for sustaining one-third of the Earth's population, as well as various deleterious environmental consequences.[2][5] Generation of hydrogen using electrolysis of water, using renewable energy, is not currently competitive cost-wise with hydrogen from fossil fuels, such as natural gas, and is responsible for 4% of current hydrogen production. Notably, the rise of this industrial process led to the "Nitrate Crisis" in Chile, when the industrials who owned the nitrate mines (most of them British) left the country — since the natural nitrate mines were no longer profitable — closing the mines and leaving a large unemployed Chilean population behind.

I hope that this little incursion into scientific knowledge will led people to think more in a scientific way than in a magic in wonderland way.

If the available overall energy is going downward, so it will for any process, especialy if it require more energy than it is currently. So I dont know how on any twist of mind can someone think that future earth inhabitant will use energy better used at enabling movement or computing to produce a chemical reaction wich is not really efficient. I mean, those windmills and Hydro plant will be kept in place with great efforts because all the infrastructure would have gone bust.

As I said on my previous post, the amonia from natural gas (or coal) wont be the thing missing in the agri business and it will not be the cause of the failure of that system. Many other things will have a more greater impact.

That was my 5 cents.

Correct me if I am wrong, but I'd guess that one does not need "grid electric" to do hydrolysis. And I'd bet that spread of $.80 to $.20 is largely accounted for in the emergy difference between "grid quality" electricity and "run of the mill" electricity. Or to put it another way, an off-grid windmill making ammonia is going to be way cheaper than using a grid tied windmill with all the associated requirements to generate electricity to grid standards and then using that electricity to make ammonia. It's like feeding beef into the compost pile when grass will do. A "point of the flame" issue.

The whole impedance mismatch of windmills (solar), lifestyle and the grid is a fascinating subject. The "flip the switch and we'll be there" meme has to die. Uses have to be tied to the times when power is available. Like those tidal mills of old - rotating shifts that matched the tides. So it's not only an issue of LESS, or even MUCH LESS, but WHEN.

cfm in Gray, ME

Ammonia can be produced from water and nitrogen gas using technology derived from solid oxide fuel cells(essentially running in reverse as you're supplying electricity). NHthree llc is trying to develop and commercialize the technology and they believe they'll be able to get 7-8 kWh/kg(3-4 kWh/lb) at lower capital requirements than haber-bosch and electrolysis.

There's also work being done searching for better catalysts that require much milder conditions than Haber-bosch.

There's nothing preventing you from deriving hydrogen gas from gasification of biomass sufficient for agriculture(as long as you don't try to use ammonia or hydrogen gas from biomass as a transportation fuel).

Because back when people were electrolyzing water for hydrogen was before the transportation of natural gas was made a reality by the invention of seamless steel pipe(1920).
http://www.scienceclarified.com/Mu-Oi/Natural-Gas.html

Also until the North Sea was developed Norway didn't have natural gas.

Also natural gas has an advantage because CH4 + H20--> CO +3H2 releases more hydrogen than 2H20--> 2H2 +O2.

Electrolysis of water is quite possible as I said but its ammonia product will be more expensive.