Healthy soil and sustainable growing

[Arzeena Hamir <arzeenahamir@shaw.ca>]

Thanks to April Reeves for forwarding this article from Western Producer. 
Sorry for the cross-posting.

I'd be interested in hearing people's comments that burying carbon with 
tillage is just as effective at storing it than the current system of no-till.

Arzeena Hamir MSc. P.Ag.
Coordinator
Richmond Food Security Society
http://richmondfoodsecurity.org
coordinator@richmondfoodsecurity.org
http://twitter.com/arzeena


Tillage not critical to carbon sequestration

A three-year study shows reduced tillage plots didn’t sequester more 
greenhouse gas than conventionally tilled plots. 


By Robert Arnason, Brandon bureau
October 13, 2011

Alberta producers who practise zero tillage have been paid millions of 
dollars over the past few years as part of an emissions trading scheme in the 
province.

The Alberta Offset System has compensated them for conservation tillage 
because the management practice is supposed to hold more carbon in the soil, 
reducing the amount of greenhouse gas in the atmosphere.

However, recent research from the University of Manitoba and work done at 
Ohio State University over the past decade suggest zero tillage is no better 
than conventional tillage when it comes to storing greenhouse gases.

Those results don’t surprise John Baker, a University of Minnesota professor 
who studies greenhouse gas balancing within agricultural systems. He has 
questioned the notion that no till sequesters more carbon than conventionally 
tilled soils.

“There are a lot of benefits to no till, in terms of reduced fuel use and 
erosion protection … so expansion of no till is a good thing,” said Baker, 
who is also a research leader with the U.S. Department of Agriculture, 
specializing in soil physics and micrometeorology.

“But I think we’re deluding ourselves a little bit if we think it’s making a 
big difference on climate change and carbon balance.”

There are experts who would strongly disagree with Baker’s conclusion, but 
Aaron Glenn, a micro-meteorologist with Agriculture Canada in Brandon, isn’t 
one of them.

“The carbon credit stuff is still going forward in Alberta … but there isn’t 
a lot of (scientific) evidence to support it,” he said.

As part of his doctoral thesis in soil science at the University of Manitoba, 
Glenn monitored the emission and absorption of greenhouse gases from no till 
and conventionally tilled plots at the university’s Glenlea Research Station 
south of Winnipeg.

Glenn and his colleagues grew a rotation of corn, fababeans and spring wheat 
from 2006-08 on four plots: two were tilled in spring and fall and the others 
farmed with no till.

The reduced tillage plots received a light harrowing at the beginning of the 
experiment to prepare the seed bed for planting.

The scientists attached instruments to one-metre-high towers to measure the 
influence of no till on carbon dioxide and nitrous oxide exchange between the 
soil and the atmosphere.

“From an atmospheric exchange perspective, this study was one of the first of 
its kind in Canada,” Glenn said.

His three year study showed reduced tillage plots failed to sequester more 
greenhouse gas than conventionally tilled plots.

“We didn’t actually find a treatment difference.”

The results were unexpected because other studies have shown that no-till 
soil stores more carbon than conventionally tilled land.

Reduced tillage is supposed to alter the composition of the soil, which leads 
to increased storage of greenhouse gases.

“By not tilling the soil, you’re not breaking up larger soil aggregates,” 
Baker said.

“Carbon that is held inside the aggregates is not as exposed to oxygen.”

The promotion of conservation tillage as part of the solution to climate 
change has been based on this link between no till and increased carbon 
storage.

However, in 2006 Baker questioned the quality of some scientific experiments 
on zero tillage and carbon sequestration.

His research review found fault in the methodologies of several studies that 
concluded reduced tillage stored more carbon in the soil. Most of them 
collected soil samples at depths of 30 centimetres or less, which Baker said 
skewed the results in favour of zero tillage.

“In essentially all cases where conservation tillage was found to sequester 
(more carbon), soils were sampled to a depth of 30 cm or less.”

He said the few studies that took soil samples deeper than 30 cm found that 
zero till soil sequestered the same, or less, carbon than conventionally 
tilled plots.

Baker has concluded that zero tillage stratifies carbon in the soil rather 
than storing more of it.

He said this might be because reduced tillage soil has more roots near the 
surface, while conventionally tilled fields have more roots at greater soil 
depth.

Partially in response to Baker’s criticism of soil sampling protocols, 
Umberto Blanco-Canqui, a graduate student at Ohio State, examined carbon 
storage at 11 sites in Kentucky, Ohio and Pennsylvania where no till had been 
practiced for years.

Most of the previous experiments on carbon sequestration had been done at the 
plot scale, and soil samples were taken at depths of 30 cm or less. 
Blanco-Canqui designed his study for the field scale and sampled the soil to 
depths of 60 cm.

A zero till field was paired with a cultivated field at all 11 locations in 
the trial, and Blanco-Canqui eventually concluded that Baker was correct.

“NT (no till) farming increases SOC (soil organic carbon) concentrations in 
the upper layers of some soils, but it does not store more (carbon) than PT 
(plow till) soils for the whole soil profile,” Blanco-Canqui wrote in his 
paper, published in theSoil Science Society of America Journal.

In the paper, Blanco-Canqui said he was surprised that no till soil in the 
trial didn’t contain more soil organic matter than cultivated soils. Plowed 
soil actually had more soil organic matter than no till soil at a few sites.

“First, (plow till) management mixes and buries residue at deeper depths than 
(no till) farming,” Blanco-Canqui wrote in an attempt to explain why plowed 
soils contained more carbon.

“Buried residues at the deepest boundaries of the plowed layer decompose at 
slower rates than surface residues because they are protected from microbial 
attack and erosion hazards, which favors (soil organic carbon) accumulation.”

Rattan Lal, who heads up the Carbon Management and Sequestration Centre at 
Ohio State and was Blanco-Canqui’s study supervisor and paper co-author, is 
known as a supporter of zero tillage and carbon sequestration, but he readily 
acknowledged that Blanco-Canqui and Baker are correct.

“Plow till, in many cases, has more carbon below the plow layer than no till 
has,” he said.

“Therefore, if you sum it up, the entire pool (of carbon), it’s not different 
in both cases.”

However, Lal said carbon trading schemes that compensate no-till farmers are 
still scientifically valid, partly because they burn significantly less 
diesel per acre than other farmers.

“But there is one other component that is very important, and that component 
is soil erosion,” he said.

“Soil erosion causes long-term changes in soil dynamics…. So when you add up 
the soil erosion part and you add up the diesel consumption … when you add up 
the water conservation … the ecosystem biodiversity … no till farmers should 
be paid more because they are avoiding emissions and sequestering (carbon).”

Baker said scientists need to study the interaction between the soil and 
atmosphere more before reaching a final conclusion on the link between no 
till and carbon sequestration.

Baker remains skeptical about the final outcome.

“I’m not optimistic that this is ever going to be a major contributor to 
mitigation of climate change. It might be one piece of a much bigger puzzle.”

Carbon facts

• Offset credits registered for zero tillage in Alberta, per tonnes of carbon 
dioxide, between 2007 and 2010: 5.08 million tonnes (CO2 equivalent)

• Total value of those offsets, assuming price per tonne of $9: $45.72 million

• Total number of acres registered for offset credits in 2010: 3.36 million 
(estimate)

• Zero till acreage in Alberta: seven million

• Zero till acres in Alberta, Manitoba and Saskatchewan: 25.0 million

Sources: Alberta Agriculture, Soil Conservation Council of Canada, staff 
research