The carbon and nitrogen cycle impacts of reverting perennial bioenergy switchgrass to an annual maize crop rotation

Authors: MOORE, CAITLIN - University Of Illinois; BERARDI, DANIELLE - University Of Idaho; BLANC-BETES, ELENA - University Of Illinois; DRACUP, EVAN - University Of Illinois; EGENRIETHER, SADA - University Of Illinois; GOMEZ-CASANOVAS, NURIA - University Of Illinois; HARTMAN, MELANNIE - Colorado State University; HUDIBURG, TARA - University Of Idaho; KANTOLA, ILSA - University Of Illinois; MASTERS, MICHAEL - University Of Illinois; PARTON, WILLIAM - Colorado State University; VAN ALLEN, RACHEL - University Of Illinois; VON HADEN, ADAM - University Of Illinois; YANG, WENDY - University Of Illinois; DELUCIA, EVAN - University Of Illinois; Bernacchi, Carl

Submitted to: Global Change Biology Bioenergy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2020
Publication Date: 10/14/2020
Citation: Moore, C., Berardi, D., Blanc-Betes, E., Dracup, E., Egenriether, S., Gomez-Casanovas, N., Hartman, M., Hudiburg, T., Kantola, I., Masters, M., Parton, W., Van Allen, R., von Haden, A., Yang, W., DeLucia, E., Bernacchi, C.J. 2020. The carbon and nitrogen cycle impacts of reverting perennial bioenergy switchgrass to an annual maize crop rotation. Global Change Biology Bioenergy. 12(11):941-954. https://doi.org/10.1111/gcbb.12743.
DOI: https://doi.org/10.1111/gcbb.12743

Interpretive Summary: Growing crops has consequences on the environment. Early in the United States, mismanagement of crops led to devastating results, such as the Dust Bowl. But consequences of agriculture have continued to presence, most notably with regard to soil carbon. Soil carbon is important for crop health. Standard row crops, which are usually tilled, result in losses of soil carbon, which impacts the long-term sustainability of an agricultural field. Growing perennial crops, however, has been shown to restore some of the soil carbon lost through tilled agriculture. This study sought to assess how quickly soil carbon gained from perennial crops, which re-sprout every year, are lost when an agricultural field is tilled and replaced with annual crops, which need to be replanted every year. The results show that soil carbon gained over ten years from perennial crops is lost within five years of switching back to annual crops. These results suggest that long-term benefits of perennial crops can only occur as long as the perennial crops are maintained in the agricultural field.

Technical Abstract: In the age of biofuel innovation, bioenergy crop sustainability assessment has determined how candidate systems alter the carbon (C) and nitrogen (N) cycles of the landscape. These research efforts revealed how perennial crops, such as switchgrass, increase belowground soil organic carbon (SOC) and lose less N than traditional annual crops, like maize. As demand for bioenergy product increases, land managers will need to choose whether to invest in food or fuel crop systems. However, little research has focused on the C and N cycle impacts of reverting purpose-grown perennial bioenergy crops back to conventional annual crop systems. We investigated this knowledge gap by measuring C and N pools and fluxes over two years following conversion of an eight year old switchgrass stand to an annual maize rotation. The converted treatment had higher ecosystem respiration (ER) than the switchgrass and maize-control treatments, which was likely driven by heterotrophic respiration of belowground switchgrass necromass. Predictions from the DayCent model indicated it would take approximately 5 years for SOC dynamics in the converted treatment to return to conditions of the maize-control treatment. N losses also increased from the converted treatment when compared to undisturbed switchgrass and maize-control. These results show that substantial C and N losses occur within the first two years after conversion of switchgrass to maize, indicating occasional rotation between perennial and annual crops would likely be detrimental to the long-term ecological sustainability of bioenergy crop systems.