Assessment of the crop coefficient for saltgrass under native riparian field conditions in the desert southwest

Limited urban water supplies in southwestern USA cause water managers and planners to re‐assess water losses and needs from consumptive water use by riparian vegetation. Here, we report on field measurements of evapotranspiration (ET) for inland saltgrass Distichlis spicata var. stricta (L.) Greene]; a once common riparian plant native to the desert southwest. The objective was to develop a saltgrass crop coefficient, Kc, similar to agricultural crop coefficients commonly used in irrigation water management. The developed Kc, in conjunction with the local climate, can then be used to assess the water savings that may be achieved in riparian zones for saltgrass versus invasive species and for use in irrigation management and scheduling of saltgrass in urban setting. The ET of saltgrass was measured in its native riparian setting located in the flood plain of the Rio Grande, north of Caballo Lake, New Mexico, in 2011 using an eddy covariance technique in the energy budget method. Total ET of 692 mm was measured during the growing season (n = 241 days) and 837 mm during the year. The American Society of Civil Engineers standardized ET for short crop (ETso) was calculated using climate data measured at the study site as 1560 mm during the growing season and 1870 mm during the year. Crop coefficients (ET/ETso) were fitted with a polynomial equation as a function of day of the year to develop saltgrass Kc function. A graphical and simplified method of computing Kc as a function of day of the year and crop season was also developed as an alternative method. Copyright © 2013 John Wiley & Sons, Ltd.