Soil Carbon – CO2

Let’s continue our discussion of Soil Health and Carbon by taking a closer look at Carbon Dioxide (CO2). Everyone is talking about atmospheric carbon and much of the discussion is based on the now famous Keeling Curve. Named after climate scientist Charles David Keeling, a quick search will come up with multiple sites with extensive charting capabilities of CO2 over time in parts per million. Below is a screen capture from NOAA Research:

Note the stair step nature of the CO2 data in the chart above. I have highlighted a small section of the chart in green, let’s take a closer look. Refer to the screen shot below:

During the growing season of the Northern Hemisphere, green plants are doing a great job of extracting CO2 from the atmosphere (drawing down CO2 levels). When our green vegetation turns brown, leaves drop and CO2 levels in the atmosphere begin to rise. Dead vegetation alone does not cause the accelerated rise shown on the graph. Unfortunately there are many acres of cropland that are tilled exposing soil carbon to oxidation and release into the atmosphere.

For the most part the up and down movement of CO2 is quite natural as part of the carbon cycle. The issue is carbon flow into the atmosphere (up) is out pacing the flows from the atmosphere (down).

Carbon Pools and Flows

In the image below note the few arrows of carbon flowing down. Looks like more sources are flowing up. Carbon “pools” (storage containers) are noted in blue.

When we chart out the flows down versus the flows up, we end up with an extra 2 gigatons of carbon flowing up into the atmosphere.

If we dig a little deeper, we find the earth soil pool accounts for most of this net flow up!

Maybe the above scenario is to simplified? Considering we are working with numbers that have nine zeros, there is probably some room for error. But I like simple.

• 750 gigatons of carbon currently stored in atmosphere
• 1,500 gigatons of carbon currently stored in SOIL
• 135 gigatons of carbon have been lost from the soil due to land use degradation (JSWC Vol. 74, No. 2, Mar./Apr. 2019)
  • Let’s reverse the annual trend of 2 gigatons of carbon leaving our soil and going into the atmosphere.
  • Let’s return some of the 135 gigatons of carbon back into our soils. Should be plenty of room there.

Our soils are hemorrhaging carbon.

Dr. Kristine Nichols, Soil Microbiologist

Regenerative Ag to the rescue!

So is it possible that Agriculture can reverse this trend? Actually yes according to Rattan Lal of the Ohio State Carbon Management and Sequestration Center.

Look again at the Carbon Flow – Sink vs. Releases chart, note that vegetation extracts about 110 gigatons of CO2 out of the atmosphere globally each year. Lal currently estimates that only 0.05% of the incoming solar energy is captured by photosynthesis each year.

WOW, that is pretty inefficient! Yet that carbon capture is enough to run our entire carbon based world (actually that is amazing).

Lal thinks that if we can just increase solar energy capture by 10% we can offset current carbon loss from fossil fuel combustion and land use change.

10% increase?

(That is moving from 0.05% efficiency to 0.055%!)

A simple example to gain 12% efficiency

In our area of Nebraska, corn and soybeans are the main crops. Typically corn is planted in April and turns brown in September. Soybeans are planted in May and turn brown in September also.

So over a 2 year growing season (Corn & Beans), there is green vegetation about 11 months (being generous) over 24 months. Remember the green and brown parts I put over the Keeling Curve above?

Adding a rye cover crop after soybeans is a very easy farming operation. If we plant a rye cover after just the soybeans we could pick up at least another 3 months of green vegetation (Oct., Nov. and Mar.) before planting corn. This would provide 14 months of green vegetation over 24 months.

No rye cover, 46% of the time, soil has green growing vegetation.

With rye cover, 58% of the time, soil has green growing vegetation.

12% increase in solar energy capture and carbon being drawn from the atmosphere into the soil.

Another plus to having the rye cover is that the soil is not exposed by tillage and carbon oxidation. Seems pretty simple and yes there are more acres going into cover crops every year. Let’s keep it up.