Evaluation and interpretation of the crop water stress index for well-watered potatoes

During the 1988, 1989 and 1990 growing seasons, canopy and air temperatures, solar and net radiation, relative humidity and wind speed were measured at 10 minute intervals during daytime hours in a field of wellwatered Russet Burbank potatoes in southeast Idaho. A linear relationship between canopy temperature minus air temperature and vapor pressure deficit (T_C-T_A = 0.2 -2.0 VPD) was developed for use in the Crop Water Stress Index (CWSI). Values of CWSI for well-watered potatoes were generally in the -0.4 to 0.4 range, and exhibited a diurnal trend of decreasing values towards midday and increasing values during the afternoon. Wind speed appeared to increase the CWSI and may account for some of the observed variability.