Wednesday, May 28, 2014

Is No-Till Enough?


May 12, 2014 -- For the past 20 years, researchers have published soil organic carbon sequestration rates. Many of these findings have suggested that soil organic carbon (SOC) can be sequestered in soil, or stored long-term, simply by switching from conventional tillage to no-till systems.
But a growing body of research indicates that no-till systems in corn and soybean rotations without cover crops, small grains, and forages may not be increasing SOC stocks at published rates.

"Some studies have shown that both conventional and no-till systems are actually losing soil organic carbon stocks over time," says University of Illinois soil scientist Ken Olson. Factors other than tillage that can cause losses include aeration, drainage, more intensive crop rotations, use of synthetic fertilizers, and lack of cover crops.

Olson and a team of senior researchers from universities in Illinois, Wisconsin, Iowa, and Ohio recently reviewed the soil science and tillage literature related to SOC sequestration, storage, retention, and loss. After examining hundreds of original research and summary papers, the scientists selected 120 papers for review and analysis.

Their review uncovered many conflicting results. For example, no-till systems on sloping and eroding sites retain more SOC in the top 0 to 15 centimeters of soil when compared to conventional systems, because the soil is disturbed less and thus erodes less. But deeper soil layers can tell a different story.
"The subsurface layers also need to be sampled and tested to the depth of rooting, or 1 or 2 meters," Olson says. "That no-till subsurface layer is often losing more soil organic carbon stock over time than is gained in the surface layer."

Another reason for inconsistent results among studies, the review found, is that different scientists use different definitions of SOC sequestration. Olson’s team proposes its definition as: the process of transferring carbon dioxide from the atmosphere into the soil of a land unit through plants, plant residues, and other organic solids, which are stored or retained in the unit as part of the soil organic matter (humus).

To claim SOC is truly being sequestered, the researchers also state that management practices must cause an increase in net SOC from a previous pre-treatment baseline, as well result in a net reduction in atmospheric carbon dioxide levels. In other words, carbon that doesn’t come directly from the atmosphere but from elsewhere outside the land unit cannot be counted as sequestered SOC. These external inputs may include organic fertilizers, manure, topsoil, or natural inputs such as sediments in floodplain and depressional soils.

The team also identified a number of other study factors that could lead to errors in reported SOC sequestration rates such as not including eroding and sloping sites in summary studies; lack of soil bulk density measurements; use of different SOC lab methods over a long-term study; natural variability not captured by the sampling scheme; only sampling plot areas once when trying to determine rates of change; and several others.

A final key finding of the team’s study relates to the method used to measure SOC rates. “In this review, both the 'paired comparison' and the 'pre-treatment' SOC methods were tested using the same plots and experiment," Olson says.

The results of this work  showed that the paired method (i.e., no-till versus conventional) overestimated SOC sequestration as compared with the pre-treatment method, where both no-till and conventional are compared to the same pre-treatment baseline. And "another flaw in the paired comparison method is that the results cannot be validated where no pre-treatment baseline is available," Olson adds.

The team therefore recommends: (1) that researchers who are trying to measure SOC sequestration rates no longer use the paired comparison method, and adopt the pre-treatment method instead, and (2) that existing long-term studies of SOC sequestration rates be stopped temporarily and sampled following the SOC sequestration protocol outlined by Olson's team.

Is no-till enough?  Not in a corn soybean rotation.  That is why many of us add wheat and barley and cover crops between cash crops.  Then we might be able to talk about increasing soil organic matter.

So much has been lost to erosion since the land was first broken.

Can we ever catch back up?

Ed Winkle

8 comments:

  1. Nice article Ed - I TA'ed Soils 101 for Ken Olson back about 20 years ago for a semester after he took over teaching it when Dr. Hassett retired.

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  2. Good. I think Ohio has the historic 50 year no-till research plots that can provide a good test of Olson's points. Rafiq Islam can do this analysis, and to some extent already has. One interesting observation from Rafiq: Bulk density changes when deep roots decay, adding organic matter to the soil. Organic matter is lighter than mineral soil particles. Your point that we need more than just a corn-soybean rotation is so true. Living roots year around!

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  3. Thanks to both of you, excellent comments. Getting this done is the hard part but it will never happen if we don't plan and carry that plan out!

    Ed

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  4. Dang, Rodale will have to republish their Regenerative Organic Agriculture paper with the new definition of soil organic carbon if it does not include the organic matter from crop residue grown in another field, like the straw in manure, but I guess it's fair, this new definition is more about real sustainability, and organics will probably keep their lead in carbon sequestration.
    http://rodaleinstitute.org/regenerative-organic-agriculture-and-climate-change/
    The Rodale paper has been covered in the news several times this week, not sure why, since it's over a month old. Probably a trigger effect when one late blog started talking about it.

    I have no clue however what Olson means by "previous pre-treatment baseline," it's not even explained in the two papers at the end of the article. Not sure if it means the levels for the previous year in full tillage, also no-till, or fallow, or whatever was grown before however it was grown.

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  5. Chimel:
    The pre-treatment SOC stock baseline is the amount of soil organic carbon in the root zone prior to the application of the treatment. Once known, the tillage treatment can be applied, such as no-till which was been applied for 20 years, the SOC stock needs to be above the pre-treatment SOC baseline.. If not no SOC sequestration happened. No-till on sloping and eroding sites often retains more SOC than MP put if both systems are losing SOC there is not SOC sequestration.MP is not at steady state.

    Ken

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  6. Randall:
    I think your idea of taking a look at the 50 year Ohio Wooster and Hoytville plots is a good one.In fact I did just that and published my findings in a comment letter in the March 3013 issue of SSSAJ. Free open access. You will find that there is little NT SOC above MP values after 50 years based on OSU researcher data and in fact the SOC are far below the forest values measure by the OSU researchers. About 35 % less after 50 years of NT treatmen than the native woods where were drained.t. Where did all the SOC go? To the water or atmosphere. 50 years of microbial activity released most of it back to atmosphere. So where is the SOC sequestration?
    Ken

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  7. Bill:
    Thanks for your vote of confidence. For those of you who have not taken my class or read the two original papers the links are provide on the American Society of Agronomy web site.

    https://www.agronomy.org/story/2014/may/mon/no-till-soil-organic-carbon-sequestration-rates-questioned

    I paid or ask the both original papers be open access for another month. The 2nd paper which was featured on the SSSA web cite will remain open access and is a long read.

    After you have read both papers please feel free to challenge but please do not do it based on only the news release.

    Ken

    The date was March 2013 for the SSSAJ comment letter. Might be good to read that and the reply from the OSU carbon group as well.

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