Evaluating potato evapotranspiration and crop coefficients in the Columbia Basin of Washington state

The current potato crop coefficient values have yet to be updated to account for newly released potato cultivars and changing climate since their inception in the 1970s. In irrigation scheduling, crop coefficients, representing three development stages, play a critical role in modeling evapotranspiration. In this study, we developed crop coefficients and evaluated crop evapotranspiration trends of five Pacific Northwest-grown russet cultivars. The field study was conducted during 2018, 2019, and 2020 growing seasons at the Washington State University Irrigated Agricultural Research and Extension Center near Othello, Washington. The potato cultivars included Alturas, Clearwater Russet, Ranger Russet, Russet Burbank, and Umatilla Russet. Crop evapotranspiration was computed using a combination of environmental and soil sensors and the soil water balance method. Crop coefficient values were developed by dividing crop evapotranspiration by reference evapotranspiration based on alfalfa. Soil water content measurements revealed that Alturas and Clearwater Russet’s water consumption was significantly higher than that of Russet Burbank during the last eight weeks before harvest. During the mid-season, crop evapotranspiration calculations of Alturas and Clearwater Russet were nearly identical, averaging 7.22 mm day−1. In contrast, the lowest crop evapotranspiration was observed in Russet Burbank, with 6.89 mm day−1. The average crop coefficient values resulting from evaluating five full-season russet potato cultivars were determined to be 0.40 during the initial stage, 0.95 during the mid-season, and 0.57 during the late-season stage. This study offers valuable information to potato growers in the Columbia Basin, enabling them to make informed decisions by providing updated crop coefficient values for determining evapotranspiration and affording them with insight into the water consumption patterns of five distinct russet potato cultivars.