About forty percent of the feedstock used in making brown anhydrous ammonia from fossil sources is used for process energy. Once produced, it takes relatively little energy to crack ammonia in the presence of a catalyst; engine exhaust heat can do it.
If you are saying that it takes more on-site energy to manufacture green ammonia from renewable sources, you would be correct, but that energy was "free" in comparison to brown ammonia's requirement for mining or drilling, transport and refining, not to mention auxillary process such as carbon-monoxide removal and CO2 sequestration, and the often ignored external costs related to health, environment and military policing of trade. Renewable production of ammonia is commonly quoted at $1000 per ton. It is not directly tied to fluctuating fossil fuel prices.
A key benefit of anhydrous ammonia is that it holds (by volume at ambient temperatures) one and a half times the amount hydrogen as liquid hydrogen. The pressure required to keep it liquid is only 150 psi - equivalent to propane. This provides a route to commercialization that is simpler and much cheaper than either liquid hydrogen or pressurized hydrogen gas at 5000 to 10,000 psi. It can also be moved inexpensively by mild steel pipeline or truck - not the case with hydrogen.
Three million tons of anhydrous ammonia are applied to fields each year by US farmers. Ammonia is not recognized as a fuel by any federal or state DOT, although it is by the USDA. It is extremely nasty stuff but the challenge of isolating it for consumer transportation may be less challenging than isolating hydrogen.
Most of what I have learned about ammonia was from here:
http://www.energy.iastate.edu/Renewa...moniaMtg09.htm