|RAJAN, NITHYA - Texas A&M University|
|CUI, SONG - Middle Tennessee State University|
|BAGAVATHIANNAN, MUTHUKUMAR - Texas A&M University|
|SCHNELL, RONNIE - Texas A&M University|
|WEST, JASON - Texas A&M University|
Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2020
Publication Date: N/A
Interpretive Summary: An Eddy Covariance system was used to monitor carbon fluxes in a rainfed cotton system. Differences in weather conditions between the two study years significantly affected carbon dynamics. Satellite remote sensing was used to corroborate Eddy Covariance observations.
Technical Abstract: Agricultural systems experience numerous management-associated events during the growing season that can significantly influence seasonal and annual carbon balances. Measurements of carbon fluxes from agricultural fields using micrometeorological techniques such as eddy covariance can improve our understanding of management and weather-driven changes in carbon budgets. In-situ carbon flux data are also valuable in developing remote sensing-based models for extrapolation of biomespecific carbon budgets to higher spatial scales. In this study, net ecosystem carbon dioxide exchange (NEE) was continuously measured for two years (2017 and 2018) from a cotton (Gossypium hirsutum) field in College Station, Texas, USA. The measured NEE was partitioned into assimilatory (GPP) and respiratory (Reco) fluxes. There were substantial differences in carbon fluxes between the two years, which were driven by variations in meteorological conditions and growth of weeds. Due to dry conditions, growing season carbon uptake in 2018 was reduced (883 g C m-2) compared to 2017 (947 g C m-2). While the growing season of 2018 was dry, the post-harvest off-season was remarkably wet with nearly 68% of the annual precipitation occurring after harvest (848 mm). This favored aggressive growth of weeds, resulting in substantial off-season carbon uptake in 2018 (374 g C m-2 in 2018 compared to 100 g C m-2 in 2017). Overall, 2017 was a net carbon source (+175 g C m-2) whereas, 2018 was a slight carbon sink (-5 g C m-2). A significant correlation was found between satellite-derived normalized difference vegetation index (NDVI) and GPP (R2 0.78 in 2017 and 0.72 in 2018). Given that correlation, it would be possible to broaden these results to the wider region by estimating GPP with satellite data.