An article has been making the rounds online about how no-till might not solve climate change.
The article, published in Anthropocene magazine, cites a study published in the journal "Geoderma" set for release with the November issue. That study has some issues. Perhaps because no-tillers are passionate and proud folks who take their preferred agricultural practices seriously, some of them are hopping mad.
"I don't want to start a holy war," one Twitter user wrote while sharing the link, in anticipation of a backlash.
Guy Swanson, whose family helped develop the Yielder Drill, and who features on our No-Till list of legends, pointed out some of the pitfalls with the article generally in an email.
For one thing, no-till today is different than no-till 50 years ago, Swanson points out.
"If the data sets are coming from a 50-year period there was no such thing as no-till until the single disc and double disc opener were developed to deep band anhydrous ammonia in 1981," he writes. "Those no-tillage deep banded acres did not begin to expand until 2004."
A review of the data furnished by researchers also raises some questions.
For example, researchers write that one of the most important factors for soil organic carbon accumulation is how much was there in the first place.
"This is supported by the fact that mean annual precipitation, together with initial soil organic carbon (SOC) concentration, were the most influential variables on the effect of no-till on SOC storage among eight selected variables," they write.
In general terms, the less carbon in the soil, the more room to put more in.
The analysis is derived from 1,061 paired comparisons from 144 studies, according to the paper.
However, the data gets thinner when you look at the initial SOC concentrations. A spreadsheet with numerical values for "starting organic concentration" is blank for 425 of those 1,061 comparisons.
That means the conclusion that no-till soil tends to collect less carbon over time is based on about 60% of the total data set.
That's good to know. I intend to vote in the fall elections based on 60% of what each candidate says. It's representative of about 5% of what they think, so democracy will be safe.
Among the 40% of surveys without starting points: the only four surveys identified as having a 50-year duration. It's not clear whether those four were from the same survey or from multiple surveys, but all are based on a sorghum-wheat rotation.
Those four 50-year results showed that no-till outperformed conventional tillage for storing soil carbon regardless of depth.
No-till management averaged for only those four surveys contained 9.54 grams per kilogram of soil organic matter to 8.26 for conventional tillage. In the top 10 centimeters, no-till averaged 12.72 grams per kilogram, while conventional tillage averaged 11.01 grams per kilogram.
I don't mean to casually discount the results of the statistical meta-analysis the authors conducted. For example, I just conducted a meta-analysis looking at those four 50-year surveys and have concluded from that sample that no-till is better than conventional tillage.
However, there are issues with carbon storage in the soil more generally that this analysis doesn't address.
Some of them are already known.
Microbes will voraciously consume any form of carbon in the soil and potentially release it back into the atmosphere. As soil expert Don Reicosky points out, "sequestration" is the wrong term for how soil and carbon interact. Carbon in the soil is ultimately destined for the atmosphere, but without tilling we can delay its return. It's not permanently gone, just pushed away from where we don't want it to go for a couple years.
Unless we till, and it comes roaring back.
The authors have also hit on a known concern for no-tillers: stratification. The less you disturb the soil, the less chance you have to mix nitrogen or any other plant nutrient deeper into it. As a result, nutrients (including carbon) tend to congregate at the top of the soil.
No-tillers frequently use cover crops with heavier and deeper roots to break up soil compaction and redistribute nutrients.
(I won't even mention the work being done to develop cash and cover crops more deeply rooted than the ones we currently use.)
Looking at the comparisons of rotations employed, which the researchers tracked, it's hard to tell where cash and cover crops begin and end. For example, one rotation, labeled "barley," is the winner of all 1,061 comparisons, with 67.10 grams per kilogram carbon after just 15 years of no-till. That kind of progress seems to point to covers, but we don't know because the researchers didn't track that. We do know that one rotation, listed as "black oat/soybean/black oat-common vetch/maize/radish oil /wheat/soybean" positively screams cover crops, but maybe someone somewhere finally developed a recipe for black-oat-and-vetch salad. If I didn't know any better, how could I tell?
Science still can't say for sure whether no-till could save us from climate change. One paper with some hole-y data probably won't change that.
Instead of bemoaning that "No-Till may not be the panacea we thought it was," Swanson suggests renaming the article "No-Tillage is Absolutely the Fastest and Most Economical Way to Store Atmoshperic Carbon by Raising Soil Organic Matter 1% Every 10 Years."
That may be a mouthful, but it does a better job conveying reality.
