Ken Olson sent me the following press release. I have previously discussed his findings here in more general terms. Olson has sometimes been criticized for discouraging No-till. Nothing could be further from the truth. He knows the importance of No-Till in soil conservation and soil quality. His concern is that claims about carbon sequestration benefits have been far over-stated or entirely misrepresented.
Date: Jan. 31, 2013
Source: Kenneth Olson,
217-333-9639; krolson@illinois.edu
New protocol recommendations
for measuring soil organic carbon sequestration
URBANA – Increased
levels of greenhouse gases, particularly carbon dioxide (CO2), have
been associated with the burning of fossil fuels, deforestation, cultivation of
grasslands, drainage of the land, and land use changes. Concerns about
long-term shifts in climate patterns have led scientists to measure soil organic
carbon (SOC) in agricultural landscapes and to develop methods to evaluate how
changes in tillage practices affect atmospheric carbon sequestration.
University of Illinois professor of soil science Kenneth Olson has used data
collected over a 20-year period at Dixon Springs, Ill., to develop a new
protocol for more accurately measuring the carbon removed from the atmosphere
and subsequently sequestered in the soil as SOC.
“Many experiments
comparing no-till to conventional tillage on similar soils have shown no-till
to have higher levels of soil organic carbon,” Olson said. “So we know in
general that no-till is often better than conventional tillage at building or
retaining more of the organic matter in the soil, which is important to crop
productivity. However, this does not mean that no-till is necessarily
sequestering atmospheric carbon. It is often just losing carbon at a lower rate
than conventional tillage.” This unexpected discovery was the result of Olson’s
use of a pre-treatment SOC measurement method that compares change in soil
organic carbon over time on the same plots using the same tillage methods.
“This protocol does not assume that soil carbon pools are at steady state
(remain the same over time), but measures SOC at the beginning of an
experiment, at intervals during, and at the end of the experiment,” Olson said.
“Comparison studies with
one treatment as the baseline (usually conventional tillage) or control and
other tillage such as no-till as the experimental treatment should not be used
to determine SOC sequestration if soil samples are only collected and tested
once during or at the end of the study,” Olson said. The comparison method
assumes the conventional tillage baseline to be at a steady state and having
the same amount of SOC at the beginning and at the end of the long-term study,
and this may not be true. No-till as the experiment treatment needs to be
compared to itself on the same soils over time to determine if SOC sequestration
has really occurred.
Olson compared two
decades of data from previously eroded Grantsburg soils on 6 percent slopes to
a 30-inch depth with low SOC content in an attempt to quantify the amount and
rates of SOC sequestration, storage, retention, or loss as a result of a
conversion from conventional tillage to a no-till system. Olson used both the
comparison and the pre-treatment SOC measurement methods on the same plot area.
His analysis revealed conventional tillage and no-till plot areas had less carbon
(C) at the end of the study than at the beginning using the pre-treatment SOC
method. According to the comparison method, no-till sequestered 4.1 tons of C
per acre for a 17 percent gain during the 20 years of the study. However, the
pre-treatment SOC method showed that the no-till plots actually lost 3.1 tons
of C per acre, a 13 percent loss in 20 years. Thus, no SOC sequestration had
actually occurred during the Dixon Springs study.
There were three major
reasons why the comparison study approach was the wrong method for measuring C
sequestration on the Dixon Springs plot area. First, the conventional tillage
plots were not at steady state and actually lost 30 percent of the C in 20
years due to erosion and SOC-rich sediment being transported off the plots. Second,
when the no-till and conventional tillage plots were sampled only once, it was
not possible to determine the rate of change over time. Last, the effect of
tillage equipment breaking down the soil aggregates increased the carbon
available to microbial decomposition and the release of C to the atmosphere as
CO₂.
“Field experiments must
be designed to more carefully measure, monitor, and assess internal and
external inputs,” Olson said. “The amount of SOC loss from soil storage during
the time of the experiment needs to be subtracted from SOC gains to determine
the change in net SOC storage. Further, soil laboratory and field methods for
quantifying SOC concentration must be refined to reduce under- and
over-estimation bias.”
Olson also recommends that
the definition of SOC sequestration include a reference to the land unit. “Soil organic carbon sequestration is
currently defined as the process of transferring CO₂ from the atmosphere into the soil
through plants, plant residues, and other organic solids that are stored or
retained as part of the soil organic matter (humus). The retention time of
sequestered carbon in the soil (terrestrial pool) can range from short-term
(not immediately released back to the atmosphere) to long-term (millennia)
storage,” Olson said. The SOC sequestration process should increase net SOC
storage during and at the end of a study to above the previous pre-treatment
baseline levels and result in a net reduction in the atmospheric CO₂ levels. I believe that the phrase ‘of a land unit’ needs to be added to
the definition to add clarity and to exclude the loading or adding of organic C
derived naturally or artificially from external sources,” Olson suggested.
Olson concluded by
saying that carbon not directly from the atmosphere and from outside the land
unit should not be counted as sequestered SOC. The
definition of SOC sequestration as defined with borders would mean any C
already in storage and transported or redistributed to the plot area or field
would have to be accounted for and does not qualify as sequestered SOC.
“Any manure from outside the plot area
or SOC-rich sediments transported and deposited from adjacent upland are just
redistributed or transported C and not really sequestered SOC,” Olson said. “That
C was already in storage and may in fact be released back to the atmosphere if
applied to the plot. For example, decomposing manure loaded on a land unit
increases the return of CO₂ to
the atmosphere and does not result in a depletion of atmospheric CO₂ , which
is the real goal. Because we often lack the ability to directly measure the
total change in the atmospheric CO₂
as a result of C loading on a plot or
field, we indirectly estimate it by measuring the change in amount of SOC being
stored in the land unit.
“These proposed
protocols are necessary to move the science forward and to attempt to address
future predicted climate trends,” Olson said. “The amount of SOC sequestered as
a result of alternative agricultural systems such as no-till and its effects on
net SOC storage changes in the soil over time and the SOC released to the water
and atmospheric pools need to be measured or calculated.”
Olson said that any
future Cap and Trade program will require SOC sequestration protocols to be established.
The method of measurement is critical if SOC sequestration is to be verified. “If
landowners are to truly sequester SOC, they must be able to prove that net
carbon gains have occurred over time in their fields and that the increased SOC
remains permanently stored in their soil,” Olson said.
“Soil organic carbon sequestration, storage,
retention and loss in U.S. croplands: Issues paper for protocol development”
was published online and will appear in the March 2013 issue of Geoderma.
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