Evapotranspiration and water stress coefficient for deficit-irrigated maize

Authors: Trout, Thomas; DeJonge, Kendall

Submitted to: American Society of Civil Engineers Journal of Irrigation and Drainage
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2021
Publication Date: 8/11/2021
Citation: Trout, T.J., DeJonge, K.C. 2021. Evapotranspiration and water stress coefficient for deficit-irrigated maize. American Society of Civil Engineers Journal of Irrigation and Drainage. 147(10). https://doi.org/10.1061/(ASCE)IR.1943-4774.0001600.
DOI: https://doi.org/10.1061/(ASCE)IR.1943-4774.0001600

Interpretive Summary: Because irrigation supplies are limited in many regions of the western U.S. and globally, deficit irrigation is widely practiced. Deficit irrigation is irrigating less than the crop needs for the purpose of reducing water use. Management of deficit irrigation requires prediction of crop water use and soil water deficits. A common method to predict crop water use is with reference evapotranspiration and crop coefficients. With deficit irrigation, a stress coefficient is also needed. A six-year deficit irrigation field study was carried out in northeastern Colorado to derive a stress coefficient for maize. Data analysis showed that an arced stress coefficient relationship modeled the data better than the commonly-used linear relationship. The data also showed that deficit irrigation reduced maize growth. Both reduced growth, which was quantified by a reduction in maize canopy ground cover, and water stress, based on the soil water deficit, must be modeled to accurately predict crop water use with deficit irrigation. With the derived relationships, irrigation managers can schedule irrigation to achieve targeted water savings.

Technical Abstract: Crop evapotranspiration under deficit soil water conditions must be quantified to accurately manage deficit irrigation and crop water stress and achieve targeted water savings. A stress coefficient is commonly used to quantify the effect of inadequate soil water on crop evapotranspiration. A six-year deficit irrigation field trial of maize in northeastern Colorado, USA was used to derive the stress coefficient for maize. Results showed that crop evapotranspiration was affected both by the effect of current soil water deficit on water uptake and stomatal resistance and by the impact of prior water stress on plant growth. Measured evapotranspiration was less than potential crop evapotranspiration when the soil water deficit exceeded 25% of the total plant available water. A curvilinear relationship modeled the measured stress coefficient better than the commonly-used linear relationship. Prior water stress resulted in a reduction in canopy ground cover which was linearly related to the basal crop coefficient. These combined effects, when incorporated into the crop coefficient times reference evapotranspiration model, were able to accurately estimate crop evapotranspiration with deficit irrigation.