Pecan (Carya illinoinensis) is one of the major crops cultivated in Doña Ana County, Las Cruces, New Mexico, encompassing a total area of approximately 14,704 ha and serving as a significant contributor to New Mexico’s economy. The USDA’s National Agricultural Statistics Service (NASS) Cropland Data Layer (CDL) reveals that pecan acreage in the Mesilla Valley, part of Doña Ana County, increased from 8778 ha in 2012 to 14,696 ha in 2021, marking a rise of 67.4%. Growing pecans, however, necessitates a substantial amount of water annually to maintain good crop quality and yield. The availability of surface water from the Rio Grande for irrigation has diminished due to prolonged drought in the region. Farmers are increasingly concerned about the availability of water for irrigation and are therefore seeking the best irrigation management practices to sustain crop production. The software used for estimating the irrigation water requirements of pecans utilizes crop coefficients as a function of cumulative heat units or Growing Degree Days (GDD), which are based on plant physiology. These GDD functions were developed over a decade ago and do not account for the recent trend of longer and warmer summer temperatures observed in the past decade, thus underestimating the irrigation water needs for pecans, particularly at the end of the growing season. This study indicates that in recent years, the duration of growing seasons has been increasing, and cumulative GDD varies from year to year. A new crop coefficient to account for these changes is proposed.
