How much Carbon have we sequestered on a tenth of an acre, in ten years, at Paradise Lot?

We (Eric Toensmeier and Jonathan Bates) have done some very rough estimates of how much Carbon has been sequestered in our garden in Holyoke, MA.

This carbon came into our system through the action of green plant photosynthesis, and through the adding of carbonaceous materials, such as woodchips, leaves, and compost (it is impossible to know which source contributed what part of the total soil carbon unfortunately). What we do know is that the system we created has locked a lot of carbon away, and unless we till the system, or burn it with fire, it should stay there for a long time.

From our calculations, we’ve sequestered 7.5 tons of Carbon in 10 years, or .7 tons per year.

So, what is the math we used to get our numbers?:
(formulas borrowed from Soil Carbon Coalition and Eric Toensmeier)

BELOW GROUND CARBON SEQUESTERED

1/10 Acre = .04 hectares

21 tones Carbon per hectare sequestered for every one percent organic matter increase in the soil

With a Logan Labs soil test, Paradise Lot went from 3% to 9% over 10 years, this equals

6% increase, so

21 x 6 = 126 t/ha x .04 hectares equals

5 tons or 1/2 ton of Carbon sequestered per year

PLUS ABOVE GROUND CARBON SEQUESTERED

In agroforestry systems: for every ton of soil organic carbon below ground, there is a 1/2 ton carbon in above ground biomass, SO,

2.5 tons of carbon above ground plus 5 tons below equal 7.5 tons, or

.7 tons/year

We’ve got the numbers, now how significant is this? We decided to do a basic comparison of this number (.7 tons/year of Carbon sequestered in the Paradise Lot 1/10 acre edible forest garden) to the CO2 emissions generated by the average person living in the U.S.A. per capita.

We could only find CO2 generated, but needed the number in Carbon, so Wikipedia says 17 tons CO2 emissions per capita U.S.A.

CO2 = 3.47 x C

17 divided by 3.47 equals

4.8 tones of Carbon emitted per person per year USA

If you grew a one acre food forest, using our methods, someone living an average carbon wasting lifestyle could easily offset their carbon use (although I’m not advocating here that we live like the average USer).

It is exciting to experience the power and abundance of diverse, multi-story, low-maintenance, temperate edible forest gardens, and realize that we are eating healthier, generating income, and locking carbon away all at the same time.

P.S. What makes these numbers very squishy is the fact that our calculations don’t account for things like the following:

-The fossil fuel carbon we’ve used building the garden: trucking in compost, bagged minerals, and chicken feed, etc
-The fossil fuels we’ve saved not buying food from the store (actually a huge number)
-The influence our garden has had on thousands of people who are also now growing gardens like ours (another huge number)
-The woodchips and leaf mulch used to create and mulch the planting beds