ARS | Publication request: USE OF CROP WATER STRESS INDEX FOR MONITORING WATER STATUS AND SCHEDULING IRRIGATION IN WHEAT

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2001
Publication Date: March 13, 2000

Interpretive Summary: In the semi-arid western United States, rainfall is insufficient for optimum winter wheat yields. Irrigation may be used to supplement rainfall, but irrigations need to be applied efficiently to minimize water stress, prevent runoff and nutrient leaching, and to be economical. Plant temperatures measured with an infrared thermometer can be used to calculate ea crop water stress index which can then be used to determine when irrigations should be applied. The crop water stress index calculation requires knowledge of the relationship between atmospheric vapor pressure deficit (the drying power of the air) and the difference between plant temperature and air temperature under well-watered conditions. This relationship is known as the non-water-stressed baseline equation, and varies with crop species and location. This study determined the non-water- stressed baseline equation for winter wheat grown in northern Colorado. The results should increase infrared thermometry's usefulness as a tool fo monitoring water stress and scheduling irrigations in winter wheat.

Technical Abstract: The crop water stress index (CWSI) is a valuable tool for monitoring and quantifying water stress as well as for irrigation scheduling. This study was conducted during the 1990 and 1991 growing seasons near Fort Collins, CO, USA. The main objective was to develop a baseline equation, which can be used to calculate CWSI for monitoring water status and irrigation scheduling of wheat. The difference in crop canopy to air temperature (Tc- Ta), measured above a crop was negatively related to the atmospheric vapor pressure deficiency (AVPD) [R2=0.88 and p=0.0001]. However, this relationship between (Tc-Ta) and AVPD can be used to develop a non-stressed baseline equation and consequently the crop water stress index (CWSI). By using non-water-stressed baseline on data collected frequently through the growing season, CWSI values may provide a valuable tool for monitoring water status and planning irrigation scheduling for wheat and which is extendable to other similar agricultural crops.