The Soils Lab is pursuing a Sustainable Agriculture Research and Education grant titled: WINSOM: Widening Interest in New Soil Organic Matter. The aim of this grant is to develop community-supported research on local farms that explores how specific land management practices affect soil organic matter (SOM; in a sense, sugar), soil respiration rates (SRR; in a sense, “soil breath”), and their quotient (SOM/SRR), something we are calling soil carbon residence time (SCRT).
All soils exhale carbon dioxide (CO2), since they are chockablock with bacteria and fungi, but not all soils exhale at the same rate. It is the correlation between these variables in the Shenandoah Valley that we wish to understand. The question we will ask time and time again is, do the soils read like a text book?
We are collaborating with Innisfree Village, Radical Roots Farm and Wildside
Farms. If you are a farmer, or a landowner, and you might be interested in partnering with JMU students to learn more about your property’s SOM, SRR, or SCRT, please contact Tony (email@example.com, (540) 568-6130) or stop by the Soils Lab in Room 7130 Memorial Hall, Harrisonburg.
In our proposal, we included some preliminary SOM, SRR, and SCRT measurements from a local farm and project cooperator, Radical Roots Farm, pictured below. Radical Roots Farm has recently been profiled as a “Be the change” story on JMU’s homepage.
WINSOM builds on work done by Nick Pence, a 2010 JMU graduate (B.S., Geology). Nick created the following poster to summarize his work. Click on it to see a full scale version of the poster.
Our Radical Roots data indicate that the approximate residence time of the carbon in the soil, that is the average time that carbon lingers in the soil before being exhaled as CO2, ranged from 1.3 to 7.4 years. The longest residence times were associated with the most clay-rich and most moist soils.
Let’s start with the upper graph, which shows data from a catena–a sequence of soils arrayed along a hillslope–we sampled along the northern fenceline of the farm. The first set of three bars on the left shows estimated annualized SRR in units of grams of carbon per square meter per year: crest, midslope, and creek (floodplain) soils all exhaled CO2 at rates of ~1300 g C/m2/y.
The second set of bars in the upper graph is the percent soil organic matter (%SOM). SOM can be measured via a method known as “Loss-on-ignition” where samples are burnt in a high-temperature muffle furnace (750 degrees, or 400 degrees C, for 6 hours), which we borrow from my colleague Liz Johnson. SOM is a keystone soil ingredient, particularly from a soil fertility perspective, and for this project provides a quick index of soil organic carbon (SOC), which we express volumetrically as a weight of carbon per volume, typically 1 square meter to a depth of 4 inches, or 0.1 m.
For Nick’s original study, we measured both %SOM and %SOC for ~35 samples in order to be able to predict %SOC from %SOM. The third set of bars shows the grams of SOCv per cubic decimeter (0.1 m3).
Finally, the last set of bars shows our calculated carbon residence time within the soil, or SCRT. This is determined by dividing the volume of carbon (SOCV; g SOCV/m2) by the CO2 flux from the soil (g C/m2/year), which we measured using the department’s Licor 8100A with a 20-cm survey chamber. The units for these estimated residence times are years, and this helps provide some data to farmers (and any landowner) that is relevant to discussions of long-term land management practices. The longest SCRT we calculated (~7 years) were associated with the Smith Creek floodplain soil, which is actually not Radical Roots property.
This upper graph provides some landscape context for how soil carbon dynamics might look with very little human intervention. The lower graph, by contrast, shows the same data, but for specific sampling locations across Radical Roots Farm. These data show greater variability in soil respiration rates, and in general, lower soil residence times. The lowest soil residence times were associated with the upper (“crest”) and lower (“swale”) portions of synergistic beds, whereas tilled beds had slightly longer SCRT, perhaps because of the mixing of clays and SOM.
Through this proposal, we hope to forge new bridges between JMU and neighboring landowners while expanding the tools and approaches for maximizing soil carbon residence times. Results will be shared with local schools (elementary, middle and high school level), churches, and civic groups to encourage greater and broader SOM sustainability.
(Tip of the hat to Fernando Perez for generating this update.)