Qunatifying evapotranpsiration and crop coefficients for cotton (Gossypium hirsutum L.) using an eddy covariance approach

Authors: Anapalli, Saseendran; Fisher, Daniel; RAO, SRINIVAS - US Department Of Energy; Reddy, Krishna

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/13/2020
Publication Date: 4/30/2020
Citation: Anapalli, S.S., Fisher, D.K., Rao, S.P., Reddy, K.N. 2020. Qunatifying evapotranpsiration and crop coefficients for cotton (Gossypium hirsutum L.) using an eddy covariance approach. Agricultural Water Management. 233:106091. https://doi.org/10.1016/j.agwat.2020.106091.
DOI: https://doi.org/10.1016/j.agwat.2020.106091

Interpretive Summary: The Mississippi (MS) river alluvial aquifer is the major source of groundwater for irrigating crops in the MS Delta region. Sustainability of irrigated agriculture in the MS Delta region is in jeopardy today due to the lack of information on water withdrawals for irrigation from the aquifer that exceed recharge rates. In order to reduce further loss of this aquifer water resource, crop-irrigation practices need to be based on accurate knowledge of water requirements of crops in response to realized weather variabilities in the field. In order to better understand this, scientists with the USDA ARS Sustainable Water Management Research Unit and Crop Production Systems Research Unit, Stoneville, MS, measured water requirements of cotton in clay dominated soils in fields farmed in the Lower Mississippi (MS) Delta, USA. For developing irrigation schedules across soils and climates other than the location in which they were measured, this study developed crop coefficients that link a crop water requirement calculated from local weather data to the measured crop water requirements. In this study, a cutting-edge science-based approach known as the ‘eddy covariance (EC) method’ was used for quantifying crop water requirements. This study is expected to help water resource managers sustain the ground water resources in the MS valley alluvial aquifer using irritated-agriculture practices that promote water conservation.

Technical Abstract: Accurate quantification of consumptive water requirements (ETc, evapotranspiration) of cropping systems is a critical prerequisite for sustainable irrigation water management applications. For applying the ETc for irrigation scheduling across soils and climates other than the location in which it was measured, it is also critical to develop crop coefficients (Kc) that link a reference crop evapotranspiration computed from local weather data to ETc. In this study, we used an eddy covariance (EC) method to quantify ETc from irrigated cotton (Gossypium hirsutum L.) in a 250 ha silty clay soil, in 2017 and 2018. In the EC experiment, an open-path infrared gas analyzer and a sonic 3-D anemometer were deployed in the constant flux layer above the cotton canopy for collecting crop-canopy water flux data. Using the measured ETc, Kc were derived for alfalfa (Kcr) and grass (Kco) reference crop ET computed from weather data. Cotton cv. Delta Pine Land 1522 was planted in the first week of May and harvested in the second week of September in both the years. Lint yield was 1269 kg ha-1 in 2017 and 1569 kg ha-1 in 2018. Measured monthly averaged daily ETc ranged between 2.5 mm in May/September to 4 mm in July in 2017, and between 2.9 mm in May and 4.4 mm in August in 2018. Maximum daily ETc in 2017 and 2018 crop seasons were 5.6 and 6.7 mm, respectively. Seasonal total ETc was 367 mm and 439 mm (on average 402 mm), respectively. Alfalfa (ETr) and grass reference crop ET (ETo) computed were 664 and 546 mm, respectively. Averaged across the two years, average daily Kcr ranged between 0.45 in May to 0.80 in August, and Kco ranged from 0.54 in May and 0.99 in August. On average, seasonal ETr was 18% more than ETo. Seasonal ETr and ETo were, respectively, 39% and 22% more than ETc. The Kc data developed will be useful for irrigation scheduling in cotton grown in similar climates and soils.