A Load of Hot Air.

Prior to the introduction of catylic converters one of the favourite was of topping yourself was to run a hose from your car exhaust, in through your car window, sit inside, start her up and wait for the carbon monoxide to do it's thing. The carbon monoxide would bind to blood haemoglobin forming carboxyhaemoglobin and prevent the exchange of carbon dioxide for oxygen. After the introduction of catylic converters suicide rates by car exhaust didn't fall (as I had presumed) it just swapped death from the effects of carboxyhaemoglobin to death by hypoxia (lack of oxygen), so obviously high levels of carbon dioxide are fatal to humans. High CO2 levels are also fatal to invertebrates, (which is a technique we used to use for fumigating seeds for storage). Given all that, why would someone interested in improving soil health want to pump something used as a fumigant underground? Sounds silly but this is what a number of farmers are starting to do, called Exhaust Emission Fertilisation the aim is to capture the exhaust gasses, cool them then inject them underground where the carbon dioxide, nitrogen oxides and other gasses:

"stimulates the biological life within the soil so the new seeding and photosynthesizing carbon dioxide from the atmosphere is done at a greater rate,”

Sounds great, it's just a pity that photosynthesis occurs above the ground. Despite all the claims there is a serious lack of scientific studies and actual evidence, the only study I've been able to find concludes:

The ANCOVA showed that the injection of exhaust did not improve or compromise crop production relative to the control. However, injecting exhaust while simultaneously applying fertiliser did initially reduce crop growth. In this season and on this soil, the crop was unresponsive to the application of fertiliser except for a small, significant increase in grain protein.

There may be some short term benefits as the acids present in the exhaust gasses react with nutrients bound up in the soil but in the long term these reserves will become depleted. Some proponents are reporting drops in soil pH. While the website promoting this system looks quite flashy it apears very short on providing actual information on how it works or any data to support their claims. I don't think I'll be buying it.