The list of very knowledgeable folk who still are pushing no-till farming as a greenhouse-gas mitigation strategy -- even though science passed them by a while ago -- includes:
- Sen. John McCain
- Princeton University* [PDF]
- The Chicago Climate Exchange [PDF]
- The Nicholas Institute for Environmental Policy Solutions [PDF]
I buried the science in the McCain post, but it deserves higher visibility. As a major review article [PDF] from Agriculture, Ecosystems and Environment, "Tillage and soil carbon sequestration -- What do we really know?" concluded:
In essentially all cases where conservation tillage was found to sequester C[arbon], soils were only sampled to a depth of 30 cm or less, even though crop roots often extend much deeper. In the few studies where sampling extended deeper than 30 cm, conservation tillage has shown no consistent accrual of SOC [soil organic carbon], instead showing a difference in the distribution of SOC, with higher concentrations near the surface in conservation tillage and higher concentrations in deeper layers under conventional tillage ... Long-term, continuous gas exchange measurements have also been unable to detect C gain due to reduced tillage. Though there are other good reasons to use conservation tillage, evidence that it promotes C sequestration is not compelling.
(Conservation tillage is "broadly defined as any tillage method that leaves sufficient crop residue in place to cover at least 30 percent of the soil surface after planting.)
This is actually not especially new research. The review article went online in June 2006, and, of course, as a review article, it was based on even earlier research -- including a 1981 (!) study that came to the same exact conclusion.
That study compared SOC and microbial biomass in long-term plowed and no-till cereal plots. They found no differences in either parameter between the two treatments when they sampled to 40 cm on an equivalent depth basis (equal mass per unit area), and concluded that no-till
has little effect on soil organic matter, other than altering its distribution in the profile.
Even worse, the review article notes this:
Studies that have involved deeper sampling generally show no C sequestration advantage for conservation tillage, and in fact often show more C in conventionally tilled systems.
D'oh!
Time to scrap no-till farming as a carbon offset or greenhouse-gas mitigation strategy.
*I confess that I relied on the Princeton "stabilization wedges" analysis myself for including this as one of the 14 or so needed to stabilize carbon dioxide concentrations below 450 ppm (see here). It was only at this April American Meteorological Society seminar, "Biofuels, Land Conversion & Climate Change," where I learned of this review article. It just goes to show you that you should always check things yourself as much as possible with primary sources. That's why I am trying to go through all of the major climate solutions (and non-solutions) this year as thoroughly as possible with numerous links to primary sources.
This post was created for ClimateProgress.org, a project of the Center for American Progress Action Fund.
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Comments
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Gar Lipow Posted 5:56 am
22 May 2008
1)Organic?
Organic no till?
Biochar? Even with it reducing other carbon absortion is it a net sequestration?
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Tasermons Partner Posted 6:04 am
22 May 2008
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Ron Steenblik Posted 6:21 am
22 May 2008
Very valuable.
These are only my personal opinions.
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Bart Anderson Posted 7:03 am
22 May 2008
No! It's time to learn more about agriculture and soil ecology.
Biological systems are complicated and we as a society have paid little attention to them.
To me this issue looks like the usual: wanting quick, simple answers for our immediate needs. Nature is jealous of her secrets and does not reveal them readily.
Bart
Energy Bulletin
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GreyFlcn Posted 7:27 am
22 May 2008
No-till is out
Land clearing is in
Nitrous Oxide is in
The evidence is turning against biofuels it would seem.
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JMG Posted 8:47 am
22 May 2008
The 5% Project
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Gar Lipow Posted 9:09 am
22 May 2008
Hmmm, I thought the carbon advantage in no-till was in not running a giant diesel-powered tiller around for a few miles (figuring that even an automated tractor-carried seed drill set up must use a lot less energy than something that plows all that ground). Can someone explain this "tilling" and then distinguish it from "no-till" for the benefit of those of us without the farm experience?
This is from extensive reading, not personal experience, but:
Non organic no-till substitutes massive herbicides for tilling, which saves energy, (even counting the energy in the herbicide) but is horrible for the environment in other ways.
Organic no-till typically rolls the weeds into the ground in a way that kills them and buries them shallowly without disturbing the roots. This still saves energy compared to a plow, especially since the roller can be in the front and the see dispenser in back of the same tracker - so only one trip not two, and not pulling a heavy plow.
3)All forms of no-till save plowing energy fertilizing energy (since no-till reduces or eliminates the need for nitrogen fertilizer.
4) There is a separate claim that no-till sequesters more carbon in the soil than plowing - separate from and above energy savings. That is the claim the study rebutted. The study was very careful to say that no-till saves energy and reduces soil erosion (also water use).
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GreyFlcn Posted 9:38 am
22 May 2008
It would keep organic carbon in the soil, and prevent it from decomposing, and leaking into the air
You could chop down all the crops above-land and turn that into biomass.
_
The first point is nearly the entire argument that people like Michael Wang make to argue the greenhouse benefits of cellulosic ethanol.
The second point is nearly the entire argument that David Perlack makes to say that we have plenty of "waste" biomass to go around.
Without this talking point, their arguments go from weak, to pathetic.
_
If you want some deep reads on no-till, might I suggest this this and this
http://greyfalcon.net/peaksoil
http://greyfalcon.net/cellulosics.pdf
http://www.stopbp-berkeley.org/CellulosicBiofuels.pdf
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GreyFlcn Posted 9:42 am
22 May 2008
Yeah, but removing the stalks/etc from the field vastly increases the need for nitrogen fertilizer.
The removal of organic residues from fields will require greater use of nitrate fertilisers, thus
increasing nitrous oxide emissions, nitrate overloading and it's devastating impacts on
biodiversity, on land, in freshwater and in the oceans. It is also likely to accelerate topsoil losses.
http://greyfalcon.net/cellulosics.pdf
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amcguire Posted 9:45 am
22 May 2008
Farmers using no-till must use herbicides while those using conventional tillage often do use herbicides in conjunction with cultivation (tillage) for weed control. Herbicides are not horrible for the environment, but erosion is.
#2:
Organic no-till is still under development and probably will not be used in large acreage extensive production of corn or wheat. It rolls a cover crop down which smothers many weeds and protects the soil from erosion
#3
No-till surely does not eliminate the need for nitrogen fertilizer - their is no substitute for the need for nitrogen in productive agriculture.
#4
No-till saves soil, first and foremost. Whether is sequesters C, no-till is still recommended for its soil saving benefits, not to mention less diesel use.
WSU Agricultural Systems Educator
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Gar Lipow Posted 11:45 am
22 May 2008
No-till can eliminate the need for external nitrogen in organic farming. As you say, rolling stalks into the field keeps some nitrogen in the soil and reduces the need for it on its own. If you do a long rotation with a grain, a legume, a fiber crop and green manure in a no-till system you can completely eliminate the need for external nitrogen fertilizers as was actually demonstrated in the "old rotation" on a no till fields in a three year rotation of cotton, corn, soybeans, rye grass and and a leguminous grass. If you can do no-till without added nitrogen with cotton you can do no-till without added nitrogen with most crops. Whether we will is another question. After all we have lots of manure to dispose of, and composted that makes a great nitrogen source and an organic nitrogen addendum. But it is important to note that organic farmers (both no-till and conventional) often see compost as a supplementary source of nitrogen, using green manures as the main source. (Green manure is when you cultivate a leguminous plant that fixes nitrogen and then plow or (in no till) roll it into the soil.) Often organic farming also using cover crops that are non-leguminous but are plowed or rolled back into the soil. This does not add nitrogen but outcompetes weeds, preserves nutrients and helps builds soil structure.
Incidentally, while carbon fixing has been used to "sell" no-till, it was originally intended as a way to prevent erosion and save labor, not as a carbon fixer.
And the hell massive use of herbicides does not harm the environment. Conventional no-till does increase use of herbicides over conventional industrial agriculture,especially round-up. Run-off of round-up and similar herbicides does a lot of harm. Mind you there is a spectrum between conventional no-till and organic. There are some examples of low-input no-till that is not quite organic, but uses long rotation and other techniques borrowed from organic farming to reduce herbicides and fertilizer use by 90% compared to conventional agriculture. That may indeed be more like using asprin than heroin.
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JMG Posted 11:51 am
22 May 2008
The 5% Project
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Gar Lipow Posted 1:01 am
23 May 2008
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