Carbon Farming: Diesel Exhaust Injection

There is a claim out that injecting tractor exhaust in to your field will mean you can skip all that expensive fertilizer, and save the planet too! It's absolute 100-proof junk science, but people want to believe it, and the 'one-born-every-minute' estimate will take in a certain number of farmers....

Here's the news item: http://www.theage.com.au/national/a-farmers-field-of-dreams-buries-climate-change-war-20091031-hqty.html

And if we can do arithmetic, and we can, here's an easily-testable quote from farmer Linklater: "It might not seem that emissions from one tractor could do a lot, but per hectare it emits 1100 kilos of carbon." Yes, he said 1100 kilos, and he said it more than once. And I'm here to tell you that Mr. Linklater's other claims (like you don't need fertilizer any more) don't make any more sense.

That 1100 kilo figure seemed bogus to me, so I did the math, with the help of a few data points from the Colorado State Agricultural Extension Service: http://www.ext.colostate.edu/PUBS/farmmgt/05006.html

1. A 100 hp diesel tractor uses 1.68 gal of diesel to plow an acre.

(Plowing, btw, uses much more fuel than most things that are done with tractors).

2. A 400 hp tractor, which Linklater has, won't use four times as much fuel, because it gets done faster, but let's say it does. So we're up to 6.72 gallons per acre.

3. There are 2.47 acres in a hectare, so that gives 16.6 gallons per hectare.

4. Diesel fuel weighs 7.0 lbs per gallon, so we're using 116.2 lbs/hectare.

5. And there are 2.47 lbs. per kilo, so we get to 47 kilos of fuel per hectare.

CONCLUSION: does anyone here think 47 kilos of fuel produce 1100 kilos of carbon emissions? The fuel is about 84.9% carbon, so if it all is 100% oxidized with two oxygen atoms for every carbon atom, you'd get (hmmm, atomic weight of carbon is 12.011, oxygen is 15.9994 ...) about 146.2 lbs of CO2.

But wait! I know what you're thinking! Maybe he meant over the course of the year, for all tractor use on the hectare. Let's see, 1100/146.2 means we're talking about passing over the field 7.5 times. But really you should figure 15 or more passes, because most things use half as much fuel as plowing, or less. And don't forget we are NOT really using four times as much fuel as a 100 hp tractor. I'll bet it would really take 30 or more passes....

Still, let's say he just might get to 1100 kilos per hectare if he captures every bit of tractor emmisions all year and injects it all. There's one other little problem with this scheme. Diesel exhaust won't fertilize. Not at all, no way.

From the data in the news story, it would seem that Linklater was applying something over 90 kilos of fertilizer per hectare. It is proposed to replace that with a substance which by weight contains:

1) 75.2% nitrogen, in the form of N2 passed through from the air, essentially inert stuff,
2) 15.0% oxygen, again from the atmosphere, what's left over from oxidizing the diesel fuel
3) 7.1% carbon dioxide, the main combustion product
4) 2.6% water vapor.

So that's 99.9% of the weight, and nothing that acts like a fertilizer yet (link, see Table 21). Oh, carbon dioxide encourages plant growth, if it's available to be absorbed in the leaves. But gaseous CO2 injected into the soil is going to do nothing but float right out of the soil, and not hang around. Though with some luck (bad) it will combine with water in the soil and makes carbonic acid and stuff. Soil acidification is not helpful. The conventional program of 90 kilos/hectare of fertilizer contained needed quantities of available nitrogen and phosphorus compounds; the 1/10th of 1% we haven't accounted for of whatever amount of exhaust is injected...does not.

It seems, though, that they were pushing this nonsense a couple of years ago in Canada. Here's an actual scientist pointing out that no matter how much exhaust is injected, this whole idea doesn't work anyway: http://www.minotdailynews.com/page/content.detail/id/514706.html?nav=5010&showlayout=0