Summary of Project

In Spring 2019, Eco-Cycle and 230 volunteer neighborhood “carbon farmers” in Boulder County launched the Community Carbon Farming Campaign as a pilot program to develop a climate solution in our own backyards. We had three goals:

1. Determine if we can use community science (aka citizen science) to measure carbon sequestration in non-agricultural urban land. Contribute data to a larger network database that was created to quantify the potential of soil carbon sequestration and rebuilding lost topsoil as a key drawdown tool to reverse climate change;
   
   
2. Educate ourselves as property managers on the best ways to manage our lawns and landscapes for carbon sequestration and resilience, and educate ourselves as consumers about regenerative agriculture and how we can support it with our purchase choices;
   
   
3. Use what we learn from this project to create a model that individuals and communities elsewhere can adopt to further the above goals.

In Year 1 (2019 growing season), we took spring baseline soil samples and sent them to our lab partner to measure the starting level of organic carbon in the soil. We repeated the sampling in the fall to vet our trial design and get a sense of the rate of change.

In Year 2 (2020 growing season), we determined from the Year 1 results that the rate of change was too slow to justify annual soil sampling. Instead, we used the LandPKS app developed by the USDA to familiarize ourselves with our own soil and the features of our yards that form our backyard microclimate.

In Year 3 (2021 growing season), we took final soil samples in the fall. Our final results look at the change in organic carbon in our soils compared to the 2019 baseline samples for each of the 5 different soil treatments used in the trials (compost, inoculated biochar, biodynamic preparation, mycorrhizal inoculant, and foliar mineral spray).

Year 3 Data

For each of the five treatments, the chart below shows the difference (delta) between the averaged fall 2021 and spring 2019 baseline data for both the treatment (test) and the control plots. The averaged values themselves are also shown in the two tables under the chart. This chart uses only complete data sets from individual trials to calculate the averages.

For simplicity, we’ve shown the data only as Soil Organic Matter (SOM). Total Carbon, the percentage of carbon that is fully stable in the soil (“carbon sequestered,” if a positive number) is 58% of SOM. Also, note that the depth filter on the right is set at 5 cm for the default view because carbon sequestration happens close to the surface first. 

To see your own results, enter your site ID—the first 3 letters of your first name, then a space, then the first 3 letters of your last name (or the person in your household who initially registered with the project) in the empty field at the upper right of the charts.

Hint: Click on the full-screen icon at the bottom right of the chart if viewing on a small screen.

Interpretation and Analysis

Why do all the numbers except for “compost test” go down? Well, it’s a bit of a mystery. We knew that 3 years was minimal to detect a meaningful change in soil carbon, but we certainly did not expect a decline. See possible explanations below, but our trial still generated interesting results when you compare the change in control plots to the change in treatment plots over the three years.

Biochar, compost, and foliar spray all show that test plots had higher levels of organic matter than the control plots at the 5 cm depth. The other two treatments do not show statistically significant differences between test and control. 

Compost is the only treatment to show a clear increase in organic matter, increasing from the 2019 baseline of 8.21% SOM by 0.52 to 8.73% SOM, and increasing by 1.1% SOM compared to the control. Compost is also the only treatment that adds significant carbon simply by applying it (compost is over 50% carbon), so we expected to be able to measure this imported carbon. Nonetheless, an increase of 1.1% organic matter demonstrates that adding compost is the quickest way to increase the organic matter in your soil.

Possible Explanations for Decreasing Carbon Values

We chose to test lawns rather than gardens specifically because grass is known to reliably store carbon and build soil as long as the soil is not disturbed. The soil scientists we’ve asked to look at this data have three hypotheses:

1. Change in lab protocol—We found a difference of -0.1% SOM when side-by-side testing the slight changes over the last three years in the carbon determination method used by our partner lab. That adjustment has been made in the above data, so obviously, that’s only a part of the story.
   
   
2. Our sampling depth changed—Judging by the volume of soil in each baggie of samples sent to the lab, it’s quite possible that we got better at sampling to the full 10cm and 20cm depths in the last three years. That’s anecdotal because we didn’t measure the volume of complete soil sample sets, but if true, we would be diluting the SOM with the deeper samples (and thus lowering the values) because SOM is usually greatest close to the surface.
   
   
3. There was an actual reduction in organic matter over the three-year trial—We’ve reached out to local soil scientists and have not found an analogous trial in our area to compare results. Thus the need for more trials like these! Did we experience climatic conditions over the trial that caused organic matter to be metabolized? This trial is over, but perhaps we’ll gain more clues with our on-farm trials just beginning.

Learn More from Our Carbon Farming Toolkit