Evapotranspiration and Yield Estimation of Spring Wheat from Canopy Temperature1

Abstract

AbstractCanopy temperature indices have been shown to be related to evapotranspiration (ET) and grain yield (Y) for many crops at various locations. The purpose of this study was to evaluate three indices at a location different from where the indices were developed. The indices were the stress‐degree‐day (SDD), temperature‐stress‐day (TSD), and the crop‐water‐stress index (CWSI), and were tested at Logan, Utah on spring wheat (Triticum aestivum L. var. Fieldwin). Planting dates were 14 Apr., 28 Apr., and 19 May 1980. Canopy temperatures in differentially irrigated plots (36 × 3 m) were measured by infrared thermometry at midday from growth stages of heading to maturity. Net radiation, wind speed, humidity, and air temperature data were collected. Neutron meter measurements were used to calculate ET. Summations of SDD (∑SDD) and TSD (∑TSD) and mean values of CWSI were calculated. Linear regression analysis for each planting showed large goodness of fit (r2 ≥ 0.93) for ET vs. ∑TSD, and for ET vs. ∑SDD (r2 ≥ 0.86). Large r2 values were obtained with Y vs. ∑TSD and Y vs. ∑SDD data. For the combined data from all plantings, r2 ranged from 0.90 for the ET vs. ∑SDD data to 0.21 for the Y vs. ∑TSD data. Slopes and intercepts of individual regression lines were significantly (α = 0.05) different. Goodness of fit of relative ET deficit with mean CWSI for the combined plantings was r2 = 0.86, and for relative Y decrease with mean CWSI, r2 = 0.78. Results indicate that SDD may be most suitable for wheat yield assessment and water management in northern Utah.