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Study Finds That No-Till Can Increase N2O Emissions in Certain Soils, Offsetting CO2 Sink

22 October 2008

Researchers at Agriculture and Agri-Food Canada (Québec City) investigating the short-term impacts of a no-tillage practice in a heavy clay soil found that within the first five years of the practice, nitrous oxide (N2O) emissions could offset the soil carbon dioxide sink. N2O is a greenhouse gas with a global warming potential (GWP) of 280 on a 20-year time horizon, compared to the baseline CO2 GWP of 1. The N2O GWP increases to 310 on a 100-year time horizon, according to data from the UN Framework Convention on Climate Change (UNFCC).

The practice of no-till has increased considerably during the past 20 years. The absence of tillage coupled with the accumulation of crop residues at the soil surface modifies several soil properties but also influences nitrogen dynamics. Soils under no-till usually host a more abundant and diverse biota and are less prone to erosion, water loss, and structural breakdown than tilled soils. Their organic matter content is also often increased. In addition, no-till is proposed as a measure to mitigate the increase in atmospheric carbon dioxide concentration.

To assess the net effect of no-till on greenhouse gas emissions, the researchers compared emissions of nitrous oxide as well as nitrogen contents and physical properties between moldboard plowed (early fall) and no-till soils near Québec City, Canada. Measurements were made during three growing seasons in a poorly drained clay and a well-drained loamy soil cropped to barley. The results of the study were reported in the 2008 September-October issue of the Soil Science Society of America Journal.

Differences in the response of nitrous oxide emissions when converting to a no-till practice between the clay and loam soils were striking. While emissions were similar in both tillage treatments in the well-aerated loam, they more than doubled under no-till in the clay soil.

Differences in emissions between tillage practices in the clay soil were observed in spring and summer but were greater and more consistent in the fall after plowing operations. The influence of plowing on nitrous oxide flux in the heavy clay soil was likely the result of increased soil porosity that maintained soil aeration and water content at levels restricting denitrification and nitrous oxide production. Accordingly, denitrification rates are usually increased in denser and wetter no-till soils and the anticipated benefits of the adoption of soil conservation practices on net soil-surface greenhouse gas emissions could be offset by increases in nitrous oxide emissions.

Our results indicate, however, that NT [no-till] can result in incremental N2O emissions that can more than offset the soil CO2 sink during the first 5 yr after adoption of this soil conservation practice in a heavy clay soil. Differences in N2O emissions between NT and MP [moldboard plowing] were greatest when differences in WFPS [water-filled pore space] between the two tillage treatments were high, suggesting that increased N2O emissions in NT were the result of enhanced denitrification. Consequently, the potential of NT for decreasing net GHG emissions may be limited in fine-textured soils that are prone to high water content and reduced aeration.

—Rochette et al. (2008)

Predicting the impacts of no-till on nitrous oxide emissions is required for a full assessment of the influence of this practice on net greenhouse gas emissions. Researchers at Agriculture and Agri-Food Canada are pursuing their investigations to understand the factors that control the mechanisms leading to nitrous oxide emissions under contrasting soil tillage practices.

Resources

  • Philippe Rochette, Denis A. Angers, Martin H. Chantigny and Normand Bertrand (2008) Nitrous Oxide Emissions Respond Differently to No-Till in a Loam and a Heavy Clay Soil. Soil Sci Soc Am J 72:1363-1369 doi: 10.2136/sssaj2007.0371

October 22, 2008 in Biomass, Climate Change, Emissions | Permalink | Comments (18) | TrackBack (0)

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The study does not make clear if it took into account external factors such as increased fossil fuel usage in conventional MP/seedbed preparation with multiple passes of heavy farm equipment. Also, if the crop residue is removed in conventioal tillage practices, there is a higher input of synthetic fertilizers; again, fossil fuel based and most likley shipped from China. Of course, NT does need more herbicide input. I would like to see a complete LCA of all external factors.

The main point of no-till agriculture is to save the soil, as I understand it. Regardless of GHG considerations, healthy soil is the basic foundation of civilization, and farming practices that permanently degrade soil are not sustainable over the long term.

To test these assertions careful comparison trials would need to be done of no-till vs ploughing with synthetic-N application. Note that even with no-till the tractor still does several passes for harvesting, seed drilling, knockdown herbicide spraying and applying P and K fertiliser. Also a bit of N in the form of ammonium salts, nitrates or urea. What happens when tractor diesel, P and K are all gone? I don't think organic farming with mules and compost can cover millions of hectares of prairie and wheatbelt country. Seems like a race between GW and PO as to which will kill us first.

The ideal combination of carbon sequestration and soil protection is probably mass-production of agrichar. It produces no N2O, is (in the long run) much more efficient to sequester carbon and can be done over and over again (while NT can sequester some carbon the first years but is not able to keep accumulating carbon for long).
Secondly, in producing agrichar, the gasses (H2 and CO) can be used to produce green energy.

I'm with the second poster up there. If you don't have good soil, it doesn't matter whether there is global warming or not. It's a natural source of NO2 anyways so what's the big deal? There are many more tons of NO2 made by cars than from the acreage of no-till farms.

Until this is replicated by others, I'd be skeptical about it's broad applicability.

Couple of things here.

N2O is a ghg produced by bacterial breakdown of organic waste.

NO2 is a combustion product and a component of urban smog.

About 90% of ghg is from natural sources. Many of the sources if pollution are natural. There is no law that says natural sources pollution. LCA would clearly show many circumstances where using biomass to get the right ratio of C:N:P:K in the soil would leaving waste C bonded with H for fuel while actually increasing food production.

To make no-till viable, the farmland needs lots of application of herbicides.

Now I don't think constantly dosing our food fields with relatives of Agent Orange is a viable long term process.

As to Global Warming: What Global Warming? There hasn't BEEN ANY for the last ten years; after only 19 years of GW that has been broadcast as the End-of-the -World,when it was only a natural and periodic climate cycle of PDO and AMO in the "warm cycle". During the past ten years of no warming we have retraced virtually all the warming of the previous 19 years.

According to the quack pseudo-scientists of AGW, that is impossible but that is what is and has happened. It goes to show that they need to go back to their drawing boards, and revise their theories of AGW via GHGs. Dr. Ferenc Miskolczi of NASA, has shown them the error of their ways, among others.

But of course, its time to shoot the messengers; by quacks like Gore and his stooges such as Hansen, Schmidt and company, who don't want their sinecures and emoluments stopped.

Here we go again!
Once more Stas shows up with this trash and once again I have to post a reply to set the record straight. I do this not to get him to see the light, that seems impossible, I do this so those people still capable of reason wont be fooled. But rather than go to the trouble of typing everything out - only to repeat myself in six weeks when he thinks we're not looking - I'll just give you guys a link or two;

http://scienceblogs.com/illconsidered/2006/04/warming-stopped-in-1998.php

http://www.cfrb.com/node/680864

Stas and ai vin are an example of two folks arguing about insignificant problems. An insignificant problem is one that you can not measure. The environmental impact of wind and water erosion is something that can be measured in air and water quality.

When you get done showing local regulators how you are protecting the air and water, then you need LCA or other computer models to demonstrate the insignificant is still insignificant.

FYI guys (I had to look it up) : "emoluments"

[15th century. < Latin emolumentum "profit, gain," literally "fee paid for grinding grain" < emolere "grind out"]

Etymology is a great discipline.

1. Soil is the foundation of agriculture.
2. Agriculture is the foundation of civilization.
3. Worldwide, soil is being lost orders of magnitude faster than it is being produced.

If you think changing from an oil economy is a big challenge, consider this: energy is relatively fungible (many sources/alternatives exist). Soil not so much.

'Traditional' agricultural practices that facilitate erosion are inherently unsustainable, and will be changed, one way (eventually abandoning the barren, degraded land) or another (pro-active change to soil-conserving practices).

One word for Nick: Israel.

We could grow our food using hydroponics; http://www.verticalfarm.com/

Stan has no belief in AGW, so why does does he go to sites and articles that specifically talk about it and he preaches his views? Because he's a TROLL.

His views should/need to be countered because in spite of a very vocal right wing minority, this is still a place for people to get centralist views. He and his ilk should not be allowed to run wild and make any accusations they want as if they're viewpoints were valid and unchallengable.

For people interested in various aspects of no-till, a comprehensive look can be seen at the scientific american site.

http://www.sciam.com/article.cfm?id=no-till

This article tries to quantify the limits of no-till operations. An important qualifier, since no-till operations, which are highly used in the US are in place largely because of gov't subsidy policy. The quantification is important in any policy decision because obviously we want to quantify the impacts our decisions have.

The nitrogen output should be viewed in light of increased artificial inputs, especially in the early stages of adoption of NT. What the article doesn't quantify is if this happened in the plots or was this happening in plots that used NT for years. Also NT, is not as suitable for northern climes as Quebec or in as heavy soils. Or the processes that denitrified the soil as more or less effected by the climatic conditions of Quebec as opposed to other areas.

Since none of this was actually quantified in the article, it is hard to judge the actual impact although it is something to consider when creating soil policy. That isn't to say that the other benefits of NT may not be worth it in themselves, just that those should be the precedent when making decisions until further studies on a broader scale can be made. For now, NT decisions should be based on it's other costs, benefits, suitability and impacts.

"Stan has no belief in AGW, so why does does he go to sites and articles that specifically talk about it..."

To provide a needed contradicting point of view.

"a needed contradicting point of view" ???

There are still people in this world who believe the world is flat, or that the Apollo moon landings were faked. At this point, with all the evidence at hand, any contradicting point of view on AGW is in the same camp as those poeple.

Herew's a contradicting point of view for you- http://keelynet.com/gravity/wright.htm
and he's got supporters- http://keelynet.com/gravity/wright1.htm

I need contacts with people who know about the risks on N2O emission and how it can be avvoided in no-till farming.
What is it in no-till farming that makes it dangerous when nature itself has been working without tilling for millions of years. It is only recently we have started tilling. What is we use compost instead of chemical fertilizers?

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