No-Till's Carbon Storing Benefits Studied

Some of you may have heard about recent attack's on no-till or conservation tillage's ability to store carbon in soils at greater rates than tilled fields.  Science can be a confusing thing, especially when it is taken out of context and looked at piecemeal.  Of course, the science on no-till's ability to store carbon in soils, just like on every other issue, will continue to evolve and should be followed.  But the clear majority of the science today indicates that no-till does indeed store carbon in many soils.

Below is a very good paper from the Consortium for Agricultural Soils Mitigation of Greenhouse Gases on no-till's ability to store carbon in soils.  I recommend it to you as an excellent overview of the research to date and as an answer to some of the no-till critics.

CASMGS paper

Tillage Effects on Soil Carbon Accumulation

July 31, 2008

 

Summary: 

Data from existing long-term field experiments provides the best source of knowledge about tillage and other production management effects on soil carbon content.  The preponderance of this data shows that that adoption of no-tillage increases soil C, relative to conventional tillage, in most U.S. cropland soils.

 

Background:

Numerous studies of replicated, long-term field experiments comparing conventional tillage (e.g. moldboard plow, chisel, disk) and no-tillage have demonstrated that most soils, following conversion to no-tillage, show an increase in soil carbon (C) content relative to tilled soils, when the measurements are integrated over the full depth of soil affected by tillage (typically the top 20-30 cm) (see reviews by Paustian et al. 1997, West and Post 2002, Ogle et al. 2005).  In general, positive soil C responses are obtained first after several years of no-till management (Six et al. 2004) and after 20-30 years, the relative rates of C accumulation tend to decline as soil C levels approach a new equilibrium level under no-till conditions (West and Post 2002).   Specific mechanisms by which the physical disturbance from tillage increases soil C loss (and conversely, that reduce soil C loss under no-till) have been proposed and supported by field and experimental evidence (e.g. Six et al. 2000, Denef et al. 2004).  On the basis of this experimental evidence, sequestration factors for reduced and no-tillage management have been developed (Ogle et al. 2005) and implemented for inclusion in the Intergovernmental Panel on Climate Change (IPCC) guidelines for national greenhouse gas inventories (IPCC 2006) and values for C credits due to no-till management have been sanctioned by the Chicago Climate Exchange (CCX).

 

At the same time, it has been long recognized that not all soils respond positively in terms of gaining C under no-till – in particular, soils with an already high content of soil C and cropland soils in cool, moist climates often do not show increases in C content under no-till compared to plow tillage; for example, this has been found for several experimental sites in eastern Canada (Anger et al. 1997).  The reasons for this lack of response to reduced tillage intensity is not yet clear, although preliminary results suggest that reduced decomposition rates of buried residues under cool, moist climates and ‘saturation’ of physically-protected soil organic C in high C soils are potential mechanisms (E. Gregorich, personal communication; D. Angers, personal communication).  However, the large majority of cropland soils in the US do not fall into this category.

 

Recently, a few researchers have raised questions about whether no-till, in general, actually leads to a relative increase in soil carbon when viewed at whole soil level, as illustrated in the papers by Baker et al.[1] and Blanco-Canqui and Lal[2].  The foundation of their arguments lay largely in the fact that most measurements of no-till vs tillage systems in long-term experiments have often only measured the top 30 cm or less of the soil profile, although several sites have been measured to depths of up to 100 cm.  These authors argue that if soil carbon contents are summed to a greater depth of the soil profile (e.g the top 0 to 60 or 100 cm) then in most cases there is no statistically significant difference between different tillage systems.  The problem with this argument is two-fold. First, it is true that the effects of no-till adoption are typically manifested in the top 20-30 cm of soil, which is the zone of soil disturbance in a tilled system!  The vast majority of tillage comparisons show no significant differences in soil carbon content below the tillage zone (Ogle et al. 2005).[3]  Secondly, because the change in soil C due to tillage management (the ‘signal’) is relatively small relative to the ‘background’ soil C content (the ‘noise’), by adding in the additional C stored in lower parts of the profile (even if differences below the plow layer are not significant), this calculation increases the ‘noise’ in the estimate such that the signal-to-noise ratio decreases and thus it is not surprising that comparisons of C content for the entire soil profile are often not significantly different.  A more meaningful determination is to utilize, as far as possible, measurements for different soil depth increments to the full depth of the soil profile and then to evaluate whether soil C contents are different below the tillage zone, and if not, then the estimates should be based on the measurements encompassing the depth of tillage, where the main effects of tillage management are manifested.  This is the procedure that has been used in developing the IPCC soil C change factors for tillage management (IPCC, 2006).

 

Other data that has been used to question whether no-till really increases soil carbon are total ecosystem C flux from eddy covariance measurements (Baker et al. 2007).  While eddy covariance (EC) techniques are a highly useful approach in C cycling research, there are several drawbacks which make them inappropriate for drawing inference about soil C changes.  First, there are only (to our knowledge) 2-3 locations in the U.S. where EC is being used to estimate ecosystem C balances for systems under no-till (Baker et al., Verma et al. 2005), thus any inferences made cannot be considered general for no-till systems.  Secondly, EC measurements have so far been for the first 2-3 years following conversion to no-till, in other words, during the transition phase between conventional and no-till when soil C increases are expected to be lowest.  Finally, the typical rates of C accumulation determined from long-term plot studies (e.g. 0.1 to 0.5 tonnes C per ha) are likely to be within the ‘error’ estimate for annual net C accumulation using EC methods, thus there is little confidence in the estimates obtained for annual soil C changes (furthermore, EC estimates to date are typically unreplicated, hence a true determination of the error associated with these annual C changes are not possible).  Hence the best method for determining soil C changes due to changes in soil management practices (including tillage) is through careful soil measurements in which the accumulated change in soil C over several years can be accurately determined.

 

An important point raised by Blanco-Canqui and Lal (2008) is that we currently lack good data on tillage effects under actual on-farm conditions.  Our best information on tillage impacts are from field experiments administered by land grant universities and by governmental research agencies (e.g. ARS)[4].  However, the approach taken in the paper by Blanco-Canqui and Lal – i.e., paired field (‘across the fence’) comparisons of tilled and no-till practices – involved a number of serious shortcomings.  First, paired comparisons – because they lack a true control – have a high degree of uncertainty.  Even if similar soil and slope conditions are chosen it is impossible to know if soil carbon contents were the same before a change in tillage practices occurred.  Secondly, in on-farm comparisons it is difficult to isolate the effect of tillage from other management variables.  In most of the comparisons described by Blanco-Canqui and Lal (2008), crop rotations and nutrient management, as well as tillage, were different within the paired comparisons – hence apparent differences between fields cannot, in fact, be attributed to tillage.  As the authors themselves point out, several of the apparent tillage differences, if real, are likely due to factors other than tillage, e.g., from pg. 697, “Unlike the NT [no-till] field, however, the PT [plow tillage] field was under winter wheat and rye cover crops, which were plowed under every year.  Thus we hypothesize that the higher SOC [soil organic carbon] with PT may have been due to the use of cover crops.  In MLRA 124, the higher SOC with PT may have been due to the use of continuous corn, a high biomass-producing crop, in contrast with the corn-soybean-alfalfa rotation in the NT field.  Annual burying of coarse corn residues in PT soils may have increased SOC at lower depths compared with the relatively low-biomass-producing rotation adopted in NT farming”.

 

Instead of using unreliable paired comparisons, new measurements of soil C change under actual on-farm conditions should be based on a resampling over time of on-farm benchmark sites, as part of a nationwide soil C monitoring network.  Such a network is currently under development as part of the National Resources Inventory (NRI) administered by USDA-NRCS (J. Goebel, personal communication).  Resources to establish and build out this network should be a high priority.  In the meantime, our data from existing long-term field experiments provides the best source of knowledge about tillage (and other management) effects on soil C – here, the preponderance of evidence supports the conclusion that adoption of no-tillage increases soil C, relative to conventional tillage, in most US cropland soils.

 

References

 

Angers, D.A., M.A. Bolinder, M.R. Carter, E.G. Gregorich, C.F. Drury, B.C. Liang, R.P. Voroney, R.R. Simard, R.G. Donald, R.P. Beyaert and J. Martel. 1997. Impact of tillage practices on organic carbon and nitrogen storage in cool, humid soils of eastern Canada. Soil Tillage Res. 41:191-201.

Baker, J.M., T.E. Ochsner, R.T. Veterea and T.J. Griffis. 2007. Tillage and soil carbon sequestration.  What do we really know? Agriculture, Ecosystems and Environment 118:1-5.

Blanco-Canqui, H. and R. Lal. 2008.  No-tillage and soil-profile carbon sequestration: An on-farm assessment. Soil Science Society of America Journal 72:693-701.

Denef, K., J. Six, R. Merckx, and K. Paustian. 2004. Carbon sequestration in microaggregates of no-tillage soils with different clay mineralogy. Soil Science Society of America Journal 68:1935-1944.

IPCC (Intergovernmental Panel on Climate Change). 2006.  2006 IPCC Guidelines for National Greenhouse Gas Inventories, Prepared by the National Greenhouse Gas Inventories Programme, Eggleston H.S., Buendia L., Miwa K., Ngara T. and Tanabe K. (eds). Published: IGES, Japan.

Ogle, S.M., F.J. Breidt and K. Paustian. 2005. Agricultural management impacts on soil organic carbon storage under moist and dry climatic conditions of temperate and tropical regions.  Biogeochemistry 72:87-121.

Paustian, K., O. Andren, H. Janzen, R. Lal, P. Smith, G. Tian, H. Tiessen, M. van Noordwijk and P. Woomer. 1997. Agricultural soil as a C sink to offset CO₂ emissions. Soil Use and Management 13:230-244.

Six, J., Elliott, E.T. and Paustian, 2000. K. Soil macroaggregate turnover and microaggregate formation: A mechanism for C sequestration under no-tillage agriculture.  Soil Biology & Biochemistry 32:2099-2103.

Six, J., S.M. Ogle, F.J. Breidt, R.T. Conant, A.R. Mosier and K. Paustian. 2004.  The potential to mitigate global warming with no-tillage management is only realized when practiced in the long term. Global Change Biology 10:155-160.

Verma, S.B., A. Dobermann, K.G. Cassman, D.T. Walters, J.M. Knops, T.J. Arkebauer, A.E. Suyker, G.G. Barba, B. Amos, H. Yang, D. Ginting, K.G. Hubbard, A.A. Gitelson and E. A Walter-Shea. 2005.  Annual carbon dioxide exchange in irrigated and rainfed maize-based agroecosystems. Agri. Forest. Meteror. 131:77-96.

 

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[1] Baker, J.M., T.E. Ochsner, R.T. Veterea and T.J. Griffis. 2007. Tillage and soil carbon sequestration:  What do we really know? Agriculture, Ecosystems and Environment 118:1-5.

[2] Blanco-Canqui, H. and R. Lal. 2008.  No-tillage and soil-profile carbon sequestration: An on-farm assessment. Soil Science Society of America Journal 72:693-701.

[3] Baker et al. (2007) argue that one way in which plowed soils could accumulate more C in deeper depths in the soil profile, compared to no-till, is if no-till results in a more superficial distribution of roots, such that comparatively more root residues are deposited in deeper soil zones under plow tillage.  Unfortunately, there are very few measurements of root distributions comparing tilled and no-tilled systems – Baker et al. (2007) cite only one study (from Switzerland) showing a deeper root distribution under plow tillage.  While this potential mechanism is worthy of further research, it does not merit rejecting the many long-term tillage comparisons showing no significant differences in soil C below the depth of tillage.

[4] However, it should be pointed out that the vast majority of agricultural field research being used for management and policy decisions in other areas (e.g. on genetics, yield, nutrient management, etc.) is also derived from controlled field research settings, and not from on-farm studies.

New Resource - A Look Ahead at the New Administration/Congress

It's a new day in Washington -- with a new Congress and a new President.  For the climate issue, that means BIG changes are in store.  It is important that the agriculture sector understand the new players that will be running the committees of jurisdiction on this issue and to note what the new President's plans are -- so that the agriculture sector can be prepared to defend its interests.

An EXCELLENT resource that I highly recommend is the Agricultural Carbon Market Working Group.  This group is comprised of farm leaders who have been working and leading on the ag-climate issue for nearly 4 years.  This group is cross-commodity and geographically diverse -- so they bring many different points of view to the issue.

Of particular value is their Resources page which contains memos and white papers on various parts of the complex ag offsets/climate issue.  Today, they have added a new paper focusing on the transition of the new administration and the a new Congress -- and what that means for the ag-climate issue.  

You can read the paper by clicking here.

Grazing Management Has Big Carbon Credit Potential

There's good news out today about how grazing can rack up carbon credits (of course, that's only if the law counts this practice).  Below is a great article that my colleague Sara Brodnax found talking about how changes in grazing practices could have a major impact worldwide on reducing GHG emissions.  

Let's hope the policy incentives are there to reward and promote this behavior rather than require it outright.  The other point to note is again, the importance of dealing with additionality in order to have a project type count as a legitimate offset.

Reuters News 

 
By David Fogarty, Climate Change Correspondent, Asia

SINGAPORE, Jan 20 (Reuters) - Simple changes in grazing practices could soak up millions of tonnes of carbon a year, helping fight climate change, improving farm productivity and earning farmers carbon credits, a scientist said on Tuesday.

But such measures needed to spread globally to more than 120 million farmers working grazing lands, such as savannah and shrubland, Andreas Wilkes of the World Agroforestry Centre in Beijing, said.

The measures also needed to be backed by the United Nations in a broader climate pact to help farmers earn carbon credits as an incentive and to pay for changes in grazing management.

Rangelands hold up to 30 percent of the world's soil carbon and span more than five billion hectares, or about 40 percent of its landmass, Wilkes and a colleague, Timm Tennigkeit, wrote in a recent report.

In grasslands, most of the carbon is in the soil, except for treed grassland, which hold a sizeable portion above ground.

Wilkes said changing grazing practices, such as replanting one or more different plant species, or sealing off portions of grassland, can boost soil carbon content.

"It depends on what the problems causing or preventing proper management are," he told Reuters in a telephone interview.

"In some places, it will be there are too many animals, so you simply reduce their number. If the soil has already begun to degrade, then maybe planting grasses is the best option.

"It's a matter of education and often also supporting conditions, such as policies. None of it is rocket science."

Improved management of grazing lands has the potential to lock away between 1.3 billion and 2 billion tonnes of carbon dioxide-equivalent worldwide up to 2030, the report says.

"Most carbon-sequestering practices also have other benefits. Increasing soil carbon content will generally improve soil fertility," it says, leading to increased livestock productivity.

At present, only U.S. farmers can earn carbon credits through improved grazing land practices.

The Chicago Climate Exchange has created an accounting standard for emissions reductions from rangelands, such as plots farmed with modern equipment that precisely positions seeds and fertiliser instead of energy-wasteful tilling, or to restore previously degraded rangeland through rotational grazing.

But the CCX's standards have been criticised as being lax and doing little to slow climate change, since farmers have carried out such practices regardless of carbon credit incentives.

Wilkes said it was crucial the next phase of the Kyoto Protocol, expected to be agreed by the end of this year, included agriculture and sustainable land management.

He said the centre was designing a pilot project together with the Food and Agriculture Organization in China.

The aim was to submit the project, together with methods to measure and verify rangeland soil carbon sequestration to the Voluntary Carbon Standard.

The International Emissions Trading Association and the World Economic Forum are among the groups backing the VCS, which aims to provide global benchmarks to ensure a credible voluntary carbon market.  

"Once the politicians can see the market is putting its money in rangelands and there are viable methodologies that everyone thinks are sound, then that may open up the opportunities at the international level," said Wilkes. 

US-CAP offsets plan

The U.S. Climate Action Partnership released its latest recommended policy actions on climate change - and an offset market is part of their blueprint.  Why is this important?  U.S.-CAP has a very impressive collection of corporate entities and environmental groups that represent a very influential block.  (To see the list of US-CAP members, click here.)

So - what did they have to say about offsets?  Below is an excerpt from their just released summary of their policy blueprint:

Offsets and Other Cost Containment Measures

Adequate amounts of offsets are a critical component of the USCAPBlueprint. Emissions offsets are activities that reduce GHG emissions that are not otherwise included in the cap. USCAP recommends all offsets meet strong environmental quality standards (i.e., they must be environmentally additional, verifiable, permanent, measurable, and enforceable). We recommend that Congress should establish a Carbon Market Board (CMB) to set an overall annual upper limit for offsets starting at 2 billion metric tons with authority to increase offsets up to 3 billion metric tons, with domestic and international offsets each limited to no more than 1.5 billion metric tons in a given year. 

In addition, the CMB should oversee a system-wide strategic offset and allowance reserve pool that contains a sufficiently large set of additional offsets and, as a measure of last resort, allowances borrowed from future compliance periods that could be released into the market in to prevent undue economic harm in the event of excessively high allowance prices, especially in the early years of the program. USCAP recommends other measures to limit allowance price spikes and volatility including unlimited banking of allowances and effective multi-year compliance period.

Now, I'm not saying this is the best policy for offsets -- but again, take a look at the LONG list of corporations (buyers of offsets) and environmental groups that have signed onto this approach.  Agricultural groups that hope to influence the offsets policy mechanism MUST engage and really understand the full scope of what an offsets market is -- what is the purpose of the product that you would be producing -- and how it fits within the larger climate legislation.  To do otherwise, risks becoming irrelevant in the formation of potentially one of the largest new commodity markets coming for agriculture.

This is a serious time - and we need serious input and all the involvement from ag groups we can get.  Yet still, some of the ag leaders who have followed this issue continue to get criticized for their mere involvement.  As if the whole issue would magically go away if all those in agriculture continue to ignore it!?!

Well, here's your choice -- you can let US-CAP fight for offsets alone -- and shape them alone, or your organization, your commodity can have a voice in shaping a product that you could CHOOSE to provide -- a product that has the potential to be the third or fourth largest crop in America!!

Ag leaders who are following this issue on the industry's behalf should be thanked - continuously.  Their lives should not be made harder because they care about the future and are willing to roll up their sleeves and find a way through this very daunting issue.

Climate Change Wrapup

Fred Yoder again, just wrapping up here at the UN Climate Change conference in Poznan, Poland. Today is the last day, and it has been a busy one. Al Gore addressed the delegation this afternoon as sort of a send-off to get ready for the final meeting in Copenhagen a year from now.

As we part from here, I do think there were many positive things that occurred. Yesterday and today, Sara Brodnax and I had meaningful exchanges with representatives from the EU, Brazil and India concerning agricultural solutions to climate change. As I said before, the ag presence here was next to nill, except for Brazil showcasing their low-carbon biofuels production. As we talked to them about soil carbon sequestration programs, it was not even on their radar screen. All who we talked to were very interested in continuing to exchange ideas and possibly develop ag-based solutions for this new treaty. In our discussions, it became apparent this type of program would benefit the developing countries as well since it could be implemented in a size-neutral way, giving everyone a stake in the solution regardless of their size or economic situation. Every country grows food.

As we leave Poznan, I can only hope we can continue to develop these new relationships and form meaningful partnerships. We need to develop ideas that would benefit all of the world's agriculture producers, and come back to the next conference with a real emphasis on agriculture as a major player. Together, we can have a real impact. As the world economic outlook looks bleak at the moment, surely we can be a driver to create efficient and economic incentives through the growing of crops worldwide while reducing our carbon footprint. At the same time I hope to continue building on those relationships with the legislative staff from the US who attended as well as we develop our own climate legislation.

So long from Poland,
Fred Yoder

Poznan Update

Hello all, it’s Sara B here in Poznan as well. Today is the beginning of the high-level discussions among the heads of state and ministers here in Poland. These sessions of the Conference of the Parties (COP) conclude several weeks of meetings on technical aspects of the agreements that are taking shape in preparation for the negotiations next year in Copenhagen.

It is very clear that everyone is watching the United States to see how we move forward with climate change under the next administration … words like anticipation and expectation come to mind. On the US side, it seems that one likely scenario is that Congress may pass some type of “placeholder” legislation in the next year to outline GHG emission reduction targets and the structure of a cap-and-trade program. This (theoretically) would create the structure needed in order for the US to participate in developing the next international treaty on climate change in Copenhagen while leaving room for future iterations and improvements.

On the ag side, there has been some limited discussion here in Poznan on agriculture and soil carbon sequestration. Many expect that agriculture will increasingly enter the negotiations as ag producer countries such as the United States and Brazil become more involved in crafting the solution to climate change. There has also been a good deal of discussion on Reduced Emissions from Deforestation and Degradation (REDD), a proposal to slow tropical deforestation in developing countries (with implications for land use change and carbon sequestration).

That's all for now, thanks for staying tuned with us here in Poland!

Reporting from the UN Climate Conference

This is Fred Yoder again reporting from Poznan, Poland at the UN Climate Conference. Well, it has been an interesting couple of days so far. There are lots of meetings to pick and choose from as to what to attend. I have been trying to learn how other countries are regarding agriculture as part of a possible solution in the reduction of GHG. Unfortunately, there are very few countries here that I have been able to find as really engaged from that aspect. Brazil has probably taken the most active role in showcasing their renewable fuel production portfolio and talking about all they are doing in their quest for reducing GHG. Really, from what I have seen so far, we have a lot of work to do in talking up the benefits and possibilities that agriculture has to offer in this arena. This afternoon we are going to attempt to talk to some representatives from the E.U. countries to get their level of interest in pursuing the development of ag credits. There has been some real progress in the protocols to include ways the developing countries can get on board with the new agreement by using credits from the forestry sector whereby over time they can transition into more specific reduction systems. Lots of dialogue, and lots of possibilities. More later.

Fred Yoder