The Possible Use of the Crop Water Stress Index as an Indicator of Evapotranspiration Deficits and Yield Reductions in Sweet Corn

Abstract The crop water stress index (CWSI) may be useful for optimal irrigation timing. This preliminary study evaluates the relationships between the CWSI and evapotranspiration (ET) and yield. The CWSI was also characterized on an hourly basis. Once-daily CWSI measurements after full ground cover was established and hourly CWSI measurements on 4 days were made in sweet corn ( Zea mays L. ‘Jubilee’) irrigation experiments in 1984 and 1985. The gradient of water applied included five irrigation levels established from 0% to 100%, with the 100% level intended to refill the root zone to field capacity, after 50% depletion of available water, at each irrigation. CWSI values, obtained hourly throughout the day, were highest between 1000 and 1700 hr . CWSI values tended to be higher in the less-irrigated plots (40% and less) than in those that received greater amounts of water (57% to 100% treatment levels). Seasonal average CWSI values (midday measurements) were closely related to the seasonal ET deficit ( r 2 ranged from 0.45 to 0.96), but there was not the expected 1:1 relationship of CWSI and ET deficit. The yield deficit of good, husked ears was also closely related to CWSI ( r 2 ranged from 0.82 to 0.93), but differences in these relationships between years and experiments indicate that CWSI measurements must be improved.