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Research Project: Bridging Project: Integrated Forage Systems for Food and Energy Production in the Southern Great Plains

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Title: Carbon and water dynamics in co-located winter wheat and canola fields in the U.S. Southern Great Plains

Author
item Wagle, Pradeep
item Gowda, Prasanna
item MANJUNATHA, PRIYANKA - Oklahoma State University
item Northup, Brian
item ROCATELI, ALEX - Oklahoma State University
item TAGHVAEIAN, SALEH - Oklahoma State University

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2019
Publication Date: 8/24/2019
Citation: Wagle, P., Gowda, P.H., Manjunatha, P., Northup, B.K., Rocateli, A., Taghvaeian, S. 2019. Carbon and water dynamics in co-located winter wheat and canola fields in the U.S. Southern Great Plains. Agricultural and Forest Meteorology. 279:107714. https://doi.org/10.1016/j.agrformet.2019.107714.
DOI: https://doi.org/10.1016/j.agrformet.2019.107714

Interpretive Summary: Net ecosystem exchange (NEE) of carbon dioxide (CO2) and evapotranspiration (ET) from co-located, paired (conventional till, CT and no-till, NT) winter wheat and canola fields were compared during a presumably favorable growing season for both crops. The magnitudes of CO2 fluxes and ET were larger for wheat than canola. In addition, wheat fields were sinks of carbon for longer periods, including winter months (December-February). As a result, large differences were observed in carbon sequestration potential between wheat and canola though both crops were strong sinks of carbon at the seasonal scale. The fluxes for both crops exhibited similar optimum values of air temperature (~22 °C for NEE and gross primary production (GPP), and ~25 °C for ET) and vapor pressure deficit (~1.7 kPa), indicating similar and well adaptation of both crops in the Southern Great Plains (SGP). However, the relationship between GPP and incident photosynthetically active radiation showed more hysteresis beyond optimum air temperature (Ta) and vapor pressure deficit (VPD – the atmospheric demand for water) in canola than wheat, illustrating greater adaptability of wheat for higher Ta and VPD. Consequently, wheat was more efficient than canola on using water and solar radiation to gain more carbon. This side-by-side comparison of minimally studied two major winter crops offers more insights into their carbon and water dynamics, and functional responses to climate in the SGP.

Technical Abstract: The magnitudes and seasonal dynamics of net ecosystem exchange (NEE) of carbon dioxide (CO2) and evapotranspiration (ET), measured using the eddy covariance (EC) technique from co-located, paired (conventional till, CT and no-till, NT) winter wheat (Triticum aestivum L.) and canola (Brassica napus L.) fields, were compared during a presumably favorable growing season for both crops. Daily peak (7-day average) NEE, gross primary production (GPP), and ET reached approximately -8 g C m-2 d-1, 16 g C m-2 d-1, and 5 mm d-1, respectively, at both CT and NT wheat fields due to uniform canopy stands. Daily peak (7-day average) NEE reached -5.19 and -4.66 g C m-2 d-1, GPP reached 12.47 and 10.86 g C m-2 d-1, and ET reached 4.7 and 4.28 mm d-1 at CT and NT canola fields, respectively. Poor recovery of canola stand in the NT field after winter damage resulted in smaller magnitudes of fluxes in spring 2017. Wheat had a larger potential as a carbon sink during winter. Larger magnitudes of CO2 fluxes and longer periods as carbon sinks for wheat caused large differences in carbon sequestration potential between wheat and canola. Fluxes showed similar responses to climatic conditions as optimum air temperature (Ta) was ~22 °C for NEE and GPP, and ~25 °C for ET, and the fluxes peaked at ~1.7 kPa vapor pressure deficit (VPD) for both crops. However, the GPP-PPFD (photosynthetic photon flux density) relationship showed more hysteresis beyond optimum Ta and VPD in canola than wheat. Ecosystem light use efficiency (ELUE) and ecosystem water use efficiency (EWUE), determined using different metrics, were higher in wheat than canola. These results indicate higher adaptability, and water and light use efficiencies of wheat than canola. This study provides an initial baseline on CO2 fluxes and ET for canola, and side-by-side comparison of eddy fluxes in two major winter crops grown in the Southern Great Plains.