Title

Eddy covariance measurements of carbon dioxide and water fluxes in US mid-south cotton production

Document Type

Article

Publication Date

4-15-2020

Keywords

Cotton, Eddy covariance, Net ecosystem exchange, Evapotranspiration, Crop coefficient

Abstract

An eddy covariance (EC) system was used over a production-scale, US mid-south cotton field in order to improve understanding of carbon and water flux dynamics in cotton production. Measurement outcomes of NEE and ET from agricultural cropping systems in the humid US mid-south may differ from measurements made in arid production regions due to variation in precipitation, relative humidity, and cloud cover. Local measurements are needed for timely irrigation water management decisions and to assess their impact on the carbon cycle. Measurements were made in a 63-ha field in Northeast Arkansas in the 2016 and 2017 growing seasons (May-October). Average daily NEE during the growing season was driven largely by gross primary production (GPP) measured at -1.80 ± 0.26 g C m−2 d-1 ranging between -13.5 and 2.4 g m−2 d-1 during 2016 and -1.97 ± 0.26 g C m−2 d-1 ranging between -11.1 and 5.9 g m−2 d-1 during 2017. Across both years the average daily GPP during the growing season was 7.65 ± 0.45 g C m−2 d-1 during 2016 and 8.33 ± 0.37 g C m−2 d-1 during 2017. GPP was lowest during emergence and post-harvest and highest from the first week of flowering (FF) stage to about 3 weeks after cutout (cessation of vegetative expansion and production of new fruiting sites). Measured ET was lowest early and late in the season, and highest from FF until cutout. Across both seasons, average ET was 3.5 ± 0.1 mm d-1, more specifically 3.3 ± 0.1 mm d-1 during 2016 and 3.6 ± 0.1 mm d-1 during 2017. Peak water use was 7.6 mm d-1 during both growing seasons. Measured ET values were similar to results from lysimeter studies conducted in humid southeastern US climates, but lower than those observed in studies in arid regions. The water use efficiency of harvest yield per evapotranspiration flux was 0.26 kg lint cotton m-3 water and 0.34 kg lint m-3 water in 2016 and 2017, respectively which 1.5–2 times those of other studies, likely due to higher yields and lower evapotranspiration measured in this study. The findings suggest that US mid-south cotton production should continue to be managed differently than other more arid US cotton production regions.

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