Assessing evapotranspiration in a lettuce crop with a two-source energy balance model

Authors: Dhungel, Ramesh; Anderson, Raymond - Ray; French, Andrew; SABER, MAZIN - University Of Arizona; SANCHEZ, CHARLES - University Of Arizona; SCUDIERO, ELIA - University Of California

Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/4/2022
Publication Date: 8/26/2022
Citation: Dhungel, R., Anderson, R.G., French, A.N., Saber, M., Sanchez, C.A., Scudiero, E. 2023. Assessing evapotranspiration in a lettuce crop with a two-source energy balance model. Irrigation Science, 41(2):183-196. https://doi.org/10.1007/s00271-022-00814-x.
DOI: https://doi.org/10.1007/s00271-022-00814-x

Interpretive Summary: The Lower Colorado River Basin (and in particular, the Yuma Valley of Arizona) are the primary source for winter vegetable production in the United States. Vegetable production is a major consumptive use of irrigation water in the highly water limited Lower Basin, so accurate estimates of vegetable crop water evapotranspiration (ET) are needed to optimize water use. However, winter vegetable crops have several major differences that can challenge ET models. These include vegetative growth that increases opposite of meteorological water demand (unlike most crops where vegetative growth occurs in sync with peak meteorological demand in summer) and shallow root systems that increase the risk of poor crop performance with suboptimal irrigation. To help improve ET estimates in these crops, we tested an energy balance model (BAITSSS) over winter-grown lettuce in the Yuma Valley. We compared BAITSSS ET estimates to measured ET from 12 fields over multiple seasons. The results showed significant soil evaporation in early season, increased transpiration as the crop grew, and overall little change in daily ET as increased vegetative cover was offset by reduced meteorological evaporative demand. The BAITSSS model estimated seasonal ET to within 1% of the measured value with relatively low daily error (1.1 mm/day). The results show that the BAITSSS model can accurately assess vegetable crop ET in the Lower Colorado Basin and would be of interest to farmers, irrigation managers, and water districts who seek to conserve increasingly constrained water supplies from the Colorado River.

Technical Abstract: Winter vegetables, including lettuce, are a significant consumptive use of water in the Lower Colorado River Basin. Precise irrigation management is needed to increase water use efficiency and reduce the negative impacts of suboptimal irrigation, including nutrient leaching, crop stress, and crop pathogens. However, lettuce has multiple features that make accurate evapotranspiration (ET) modeling difficult, including asynchronicity with meteorological evaporative demand, short growing seasons, and a shallow root zone that increases the risk of using an incorrect ET value. To improve ET modeling and understand applied irrigation effectiveness for lettuce in this region, we used an energy and water balance bio-physical model, Backward-Averaged Iterative Two-Source Surface temperature and energy balance Solution (BAITSSS) on arid farmlands in the lower Colorado River basin. The study was conducted between 2016 and 2020 at twelve eddy covariance (EC) sites in lettuce with a wide range of soil physical properties. BAITSSS was implemented using ground-based weather and irrigation data, and remote sensing-based vegetation indices (Sentinel-2). The model accuracy varied among sites, with a mean cumulative seasonal ET of'~'3% and mean RMSE of 1.1 mm d-1 when compared to EC. The results showed that accurate timing and amount of applied water (irrigation and precipitation) were critical to capturing ET spikes right after irrigation and tracking the continuous decrease of ET. This study highlighted the dominant factors that influence the ET of lettuce and how BAITSSS can improve ET modeling for irrigation management.