Oklahoma's Red Dirt links family legacy to a sustainable future

Switchgrass is a deep-rooted perennial native to the US prairies and an attractive feedstock for bioenergy production which may provide a potential mechanism to accumulate soil carbon. However, the impacts of switchgrass establishment on highly eroded marginal lands are poorly understood.

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First light of dawn seen through the fully grown switchgrass field taken during an early summer morning sampling trip. 

Switchgrass roots grow deep, family connections to the soil grow deeper. My great grandfather, Robert Miller on my mother’s side, was a tenant farmer from Kingston, Oklahoma. He and some of his family made the difficult choice to stay in Oklahoma during the 1930s while the ecological disaster known as The Great American ‘Dust Bowl’ ravaged the central prairies and the southwestern US. A combination of severe drought, dust storms, and years of poor land management and soil cultivation techniques would lead to devastating levels of topsoil erosion. It is estimated that roughly 40 million hectares of land (Worster, 1982; Baumhardt, 2003; Schubert et al., 2004) were affected and that this catastrophe generated many sites that remain ‘marginal’ for agricultural development due to low soil nutrient quality. In fact, it has been estimated that globally up to 133 Pg of carbon (Sanderman et al., 2017) have been lost from the soil due to agricultural land uses. Prompting the need for new land usage methods to try and build back the soil carbon debt that has accumulated over centuries. Luckily, there may be a solution for some of these sites to both replenish the soil carbon stocks and prevent further erosion through the cultivation of deep-rooted perennial grasses. 

With uncertainty looming for how climate change will affect our planet we can look to the past for examples from history to try and influence our current public policies and practices to meet future sustainability goals. A) photographed here is Robert Miller and his wife Ethel Miller my great grandparents from Kingston, Oklahoma. B) Shown here some of the devastation brought on by severe dust storms during the Great American Dust Bowl of the 1930s in Oklahoma. Photo by the Library of Congress.

Unfortunately, I never met my Great Grandfather; he passed long before I got a chance to meet him. I would like to think that he would be proud to know that his legacy of working the soil has persisted. Although now that legacy moves towards helping establish the sustainability of future land management practices in the famous ‘Red Dirt’ of his home state. Yet, the crop we focused on in our study has an entirely different use than crops he would have grown.

Sampling our two contrasting field sites in southern Oklahoma took place over 17 months starting in the summer of 2016 and continuing until the winter of 2017. A) A view of the sandy-loam soil texture site near the Texas border with switchgrass in the late summer of 2016. B) A view of the clay-loam soil texture site located just north of the town of Ardmore in the summer of 2016. C) A photograph of me next to the switchgrass in the summer of 2017. 

Switchgrass is a tall deep-rooted native grass that has garnered a lot of attention over the years for its ability, once established, to yield high above and belowground biomass in nutrient-limiting environments. However, researchers still have a limited understanding of the effect switchgrass cultivation has on these eroded marginal land sites.

Our field sampling consisted of 21 replicates per plot and plots both with and without switchgrass in these two contrasting soil types over two growing seasons. A) A breakdown of the parameters measured in our study which included real-time in situ soil trace gas measurements, tracking soil chemistry changes, and monitoring the soil microbiological communities over time. B) Diagram of the processing of the trace gas data collected in the field. C-D) Arthur Escalas monitoring trace gas fluxes via the cart-mounted Picarro Trace Gas Analyzer in the field. 

To address this, we investigated the belowground chemical and microbiological impacts of switchgrass establishment at two contrasting marginal soil types along with monitoring the consequences of soil greenhouse gas emissions over 17 continuous months. At our sandy-loam site, we saw a 27% increase in topsoil carbon levels, but not at the clay-loam site. Instead, the clay-loam site was marked by higher CO2 production and a reduction of microbial diversity (both alpha and beta). Changes observed in the microbial communities at each site may reflect different survival strategies that switchgrass employs in the recruitment of specific taxa to its rhizosphere based on geochemical differences found between the two sites. Interestingly, total methane consumption was reduced by 39 to 47% for each site with switchgrass, and periods of low methane emissions were observed. Thus, implying that methane fluxes should be accounted for to fully evaluate the sustainability of switchgrass cultivation at these marginal sites. Our results suggest that sandy-loam marginal sites may provide more sustainable benefits during switchgrass establishment.

References

  1. Schubert SD, Suarez MJ, Pegion PJ, Koster RD, Bacmeister JT. On the cause of the 1930s Dust Bowl. Science. 2004;303:1855–9.

  2. Worster D. Dust bowl: the Southern plains in the 1930s (Oklahoma and Kansas). Dust bowl South Plains 1930s (Oklahoma Kansas). Oxford University Press; 1982; p. 15–50.

  3. Baumhardt LR. Dust Bowl Era. In: Encyclopedia of water science. New York: Marcel Dekker; 2003.

  4. Sanderman J, Hengl T, Fiske GJ. Soil carbon debt of 12,000 years of human land use. Proc Natl Acad Sci U S A. 2017,

Colin Bates

Research Assistant , The University of Oklahoma