Lettuce evapotranspiration and crop coefficients using eddy covariance and remote sensing observations

Authors: French, Andrew; SANCHEZ, CHARLES - University Of Arizona; Hunsaker, Douglas - Doug; Anderson, Raymond - Ray; SABER, MAZIN - University Of Arizona; Czyzowska-Wisniewski, Elzbieta

Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2024
Publication Date: 4/1/2024
Citation: French, A.N., Sanchez, C.A., Hunsaker, D.J., Anderson, R.G., Saber, M.N., Czyzowska-Wisniew, E.H. 2024. Lettuce evapotranspiration and crop coefficients using eddy covariance and remote sensing observations. Irrigation Science. (2024). https://doi.org/10.1007/s00271-024-00921-x.
DOI: https://doi.org/10.1007/s00271-024-00921-x

Interpretive Summary: Lettuce is an economically important crop in the USA Southwest that relies on effective irrigation to meet the crop’s water use requirement while minimizing yield and lettuce quality losses caused by over irrigation. However, lettuce crop water use information is nearly five decades out-of-date and cannot be relied upon to provide guidance needed for precise water management. To address this shortcoming, ARS scientists at Maricopa, Arizona, conducted research to establish and update current crop water use information; and to develop related tools to promote efficient irrigation management in this water-limited region. The studies were undertaken on 12 commercial sites in Yuma, Arizona, USA between 2016 and 2020. Findings indicated that the seasonal lettuce crop water use requirements are greater than suggested in previous technical reports. The study also updated lettuce crop coefficients that are used to estimate daily water use. Heat unit results from the study make possible better forecasting of lettuce growth stages and total irrigation required. Outcomes from this study will be important for vegetable crop growers, water managers, and irrigation districts concerned with effective use of freshwater.

Technical Abstract: Lettuce (Lactuca sativa L.) is a high-value crop for irrigation districts in the low deserts of the USA Southwest. To ensure maximal crop quality, negligible soil salinity stress, minimal nutrient loss and reduced pathogen susceptibility, lettuce irrigation must meet, but not exceed, crop water use requirements. Lettuce crop water use information is outdated in this region: prior studies were conducted at least four decades ago (1960-1980) and do not represent current varieties, management practices, and climate. To address this shortcoming, we studied 12 commercial sites in Yuma, Arizona, USA between 2016 and 2020 to update lettuce water use requirements and crop coefficients. The study measured crop evapotranspiration (ETc) using eddy covariance observations at 8 iceberg and 4 romaine sites, where planting dates varied throughout the fall. Observed ETc and remote sensing data were used to model the daily soil water balance and single and dual crop coefficients (Kc, Kcb, Ke). The analysis was supported by lettuce crop height estimates and fractional vegetative cover (fc) via remote sensing. Days to maturity averaged 75±15 and 89±12 days for romaine and iceberg, respectively. Seasonal lettuce ETc averaged 278±24 mm and cumulative irrigation applied averaged 340±78 mm. Lettuce crop coefficients varied from 0.90±0.13 to 1.19±0.11 for Kc and from 0.20±0.05 to 1.01±0.11 for Kcb for the initial and mid-season growth stages, respectively. Average days to maturity were 1134 and 810 C-days for growing and enhanced degree day metrics. The study updates information that can guide more efficient lettuce irrigation management.