There is theoretically a lot of Nitrogen gas in diesel exhaust like 80%

http://www.pca.state.mn.us/hot/legislature/reports/2001/at-appendix-e.pdf

Theoretically even an 8 litre diesel engine should exhaust about 500 lbs of N2 per acre along with irrelevant mass quantities of nitrogen oxides if you are considering use as fertilizer. Nitrogen oxides seem to be around 160 ppm. Problematic from an environmental point of view but no way to fertilize your crop.

But that's the whole problem. It is mostly in the form of the very stable N=N molecule where the Nitrogen atoms are covalently sharing an electron and completing each others valence electron shells

http://en.wikipedia.org/wiki/Nitrogen_gas#Reactions

The N is there but it is not in a form chemically that can be incorporated to the soil practically. It is also lighter than air on top of being non reactive. Not the recepe for good sealing.

However most of the air we breath is Nitrogen also so you could just blow fans at the field.

I think the concept of using exhaust gas as Nitrogen fertilizer in this way just doesn't make any physical sense. But I do think burying your exhaust emissions in the field and selling the carbon credits could be good for the environment and your pocketbook especially the way federal regulations are going. Do I honestly think you can seal it? Maybe you could use the soil to trap particulates and that would not be a bad thing at all. Probably a good idea even. Think about how hard it is to seal even the highly chemically reactive ammonia fertilizers.

It takes energy to get nitrogen into an unstable form so that when you put it back into the soil it is reactive. There is no free lunch. I was on an NSF grant for undergraduates in Physics one summer and a professor made us read through papers sent in by lay people who would send in papers, often puporting to disprove some central principle of physics, and find out what was wrong with them. This feels like that to me. On the surface it sounds like a plausible idea, a really great idea, but just not quite physcially sensible.

This is like a great Brita filter for your exhaust which is totally smart, but probably not more.

So what they're doing if you look at the website is taking the gross emissions emitted by the farmers tarctor (which is actually sealing some fractional percentage of it) and selling the credit to some factory in China so they have the moral authority to pollute our atmosphere even more? And they conveniently want to market the carbon credits on their own exchange? It just doesn't smell right.