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ARS Home » Plains Area » El Reno, Oklahoma » Oklahoma and Central Plains Agricultural Research Center » Livestock, Forage and Pasture Management Research Unit » Research » Publications at this Location » Publication #427711
Research Project: Integrated Research to Enhance Forage and Food Production from Southern Great Plains Agroecosystems

Location: Livestock, Forage and Pasture Management Research Unit

Title: Carbon and water dynamics of Old World bluestem in the U.S. Southern Great Plains

Author
item Wagle, Pradeep
item XIAO, XIANGMING - University Of Oklahoma
item Gunter, Stacey

Submitted to: Ecosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2026
Publication Date: 5/17/2026
Citation: Wagle, P., Xiao, X., Gunter, S.A. 2026. Carbon and water dynamics of Old World bluestem in the U.S. Southern Great Plains. Ecosphere. 17(5). Article e70668. https://doi.org/10.1002/ecs2.70668.
DOI: https://doi.org/10.1002/ecs2.70668

Interpretive Summary: Forage production in the U.S. Southern Great Plains (SGP) has diversified through the cultivation of millions of hectares of different cultivars of old world bluestem (OWB, Bothriochloa spp., perennial, warm-season grass) on marginal, degraded, and highly erodible pastures and rangelands. This study analayzed four years (2021–2024) of continuous eddy covariance measurements in an OWB pasture located in central Oklahoma to quantify the dynamics of carbon dioxide (CO2) fluxes and evapotranspiration (ET) and to examine the factors that influence these processes. Key findings show that aboveground biomass varied significantly from year to year, ranging from about 3 to 9 t ha-1. The pasture released up to about 6 mm d-1 of water (ET). Daily gain of carbon (net ecosystem CO2 exchange, NEE) by the pasture reached up to 8 g C m-2 d-1. During the colder, non-growing months (November to March), the water released by the pasture remained consistently low (<20 mm month-1), regardless of the rainfall amounts. However, in the warmer growing season (April to October), ET was much higher and more varied. The OWB pasture functioned as a carbon sink (i.e., absorbed more CO2 from the atmosphere than it released) for about three to five months each year, depending on the rainfall. Annually, the pasture's overall carbon balance varied widely, sometimes acting as a net carbon sink (absorbing CO2) and sometimes as a net carbon source (releasing CO2), highlighting its sensitivity to rainfall variability. The strong correlation between satellite-derived vegetation greenness (i.e., enhanced vegetation index, EVI), carbon exchange, and water use illustrates the great potential of satellite-derived EVI for monitoring ecosystem productivity and estimating CO2 fluxes and ET over large areas of OWB.

Technical Abstract: Forage production in the Southern Great Plains (SGP) of the United States has diversified through the cultivation of millions of hectares of old world bluestem (OWB, Bothriochloa spp.), a perennial warm-season grass. This study analyzed four years (2021–2024) of continuous eddy covariance measurements in an OWB pasture located in central Oklahoma. The study period included a range of weather conditions, covering both drought years and deluge. The main objectives were to quantify the dynamics of carbon dioxide (CO2) fluxes and evapotranspiration (ET) and to examine the factors that influence these processes. Aboveground biomass showed significant interannual variation, with peak biomass ranging from ~3 to 9 t ha-1. Daily peak ET, net ecosystem CO2 exchange (NEE), and gross primary production (GPP) were about 6 mm d-1, -8 g C m-2 d-1, and 15 g C m-2 d-1, respectively. During the non-growing season (November-March), monthly ET remained similar and consistently low (<20 mm) despite substantial fluctuations in monthly rainfall. Higher and more variable monthly ET were recorded during the growing season (April-October). The pasture acted as a carbon sink for three to five months each year, depending on the amount and distribution of rainfall. The OWB pasture functioned as a carbon sink during the growing season, with NEE sums ranging from -55 to -380 g C m-2. The annual NEE sums exhibited greater variability, ranging from 58 (carbon source) to -228 g C m-2 (carbon sink). Nevertheless, seasonal to annual ET (0.86–0.90) and GPP (0.89–0.94) remained remarkably consistent. The strong correlation between enhanced vegetation index and fluxes underlines the critical role of vegetation greenness in regulating OWB's carbon exchange and water use. The results also confirm the accuracy of satellite-derived vegetation indices for OWB, indicating their potential for monitoring ecosystem productivity and estimating CO2 fluxes and ET over large areas.