Crop Insurance Today First Quarter 2021 - 12

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What's Growing On?

Farming Carbon-a brief look at
carbon and agriculture
By Dr. James Houx, NCIS

Carbon is at the forefront of discussions
concerning greenhouse gases (GHG's), climate change, and agriculture's role in the future of a green economy. Recently, it is difficult
to find a sentence with carbon that does not
also include agriculture. For the foreseeable
future, these two words will be most likely
intertwined in agriculture policy decisions
aimed at reducing greenhouse gases and battling climate change worldwide.
On a relative scale, U.S. agriculture is reported
to account for 10 percent of the total U.S. GHG
emissions. (Figure 1). Current discussions are
largely focused on how agriculture can be used
to offset GHG emissions and reduce its relatively
small emission footprint. While some view this as
Figure 1

Total Greenhouse
Gas Emissions in the
U.S. during 2018.

Source: U.S. EPA

FIRSTQUARTER2021

a panacea for GHG reductions, others are taking
a more cautious and realistic approach as to how
much of an impact agriculture can have. Irrespective, this is not a bad spot for agriculture to be in.
What is agriculture's role in all this and how
can agriculture contribute to the reduction in
GHG's? The buzzword here is carbon sequestration-or trapping carbon in annual and perennial plants, trees, decaying residues, and largely
in the soil beneath our nations row cropping systems. However, sequestration does not end there
as there are much broader implications regarding
soil health, conservation, and implementation of
progressive farming technologies.

The carbon cycle of life

Carbon is the backbone of life. It is also a
drifter-transient in our atmosphere and typically only stopping for brief stays. This movement
of carbon through life (and death) and the interludes through air, water, and earth has implications for GHG emissions depending on how long
carbon stays in one place, and how willing it is to
stay for a longer time. This movement of carbon
is called the carbon cycle and a discussion of sequestration begins here (Figure 2).
Carbon in its most well-known form, carbon
dioxide (CO2), is an important part of our atmosphere, but when there is too much in the air it
can create problems. Although CO2 accounts for
roughly 0.04% of our atmosphere, its levels have
been rising at an increasing rate and this rise is
correlated with increasing global temperatures
and climate instability, referred to as the " greenhouse effect " .
Carbon is taken in by plants as CO2 through
the pores in leaves, stems, and other plant organs.

This phenomenon is known as photosynthesis
where CO2 is converted into carbohydrates. It
is here that CO2 is fixed or captured within the
plant to produce a multitude of organic carbon
compounds necessary for plant growth and metabolism. The compounds are used to construct
cell walls and are the backbone of the structure
of plants from roots to stems to leaves to grain. In
fact, carbon, along with its carbohydrate components, hydrogen, and oxygen, make up over 9095 percent of the dry weight of most plants.
However, all plant tissues die, and most of the
carbon that was fixed or captured within tissues
is quickly " cycled " back to CO2. This happens as
the dead plant matter is consumed by microorganisms, and invertebrates, on and below the
soil surface. These organisms also expire, and in
turn the initial plant carbon is " turned over " once
again and consumed by other organisms. As the
process continues, more CO2 is released as the
carbon compounds are oxidized by microorganisms. This phenomenon, called soil respiration,
is the combined respiration of millions of organisms that are consuming the decaying organic
carbon that for the most part originated from
plants. This carbon is called active carbon, and
it is considered unstable because once the carbon
inputs cease, the amount of active carbon in the
soil declines as the microorganisms eventually
cannibalize the remaining active carbon pool.
Irrespective, active carbon cycling is the first step
in meaningful carbon sequestration in agriculture ecosystems.
A small fraction of active carbon that enters
the soil becomes " trapped " in stable, relatively
large, recalcitrant carbon compounds that are resistant to further soil microbial decomposition.

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Crop Insurance Today First Quarter 2021

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