Estimating Cotton Water Stress for Production Management
Apr 18, 2019
Crop water stress evaluation is essential for accurate irrigation scheduling. Cotton was grown in 1997 using four irrigation levels where canopy temperatures (TC) were continuously measured with infrared thermometers. Water level treatments were rainfall (WL1)-, 1/3 ET (WL2), 2/3 ET (WL3), and 1.0 ET (WL4). This report compares the accuracy of different stress indices for describing crop water stress. The first method for estimating water stress was the daily summation of stress time (ST) when TC exceeded 28°C. The second method was the Crop Water Stress Index (CWSI) that included a theoretical procedure, CWSI-T, and the empirical method, CWSI-E. ST was compared for three daily periods- Midday, Daytime and Entire Day defined by threshold levels of net irradiance and air temperature. Cotton ST for the Daytime and Entire Day increased as the amount of water applied declined and was significantly different among all water levels. The CWSI-T and CWSI-E values also declined as the quantity of water applied increased. CWSI-E was more accurate than CWSI-T because its stress values for the well-watered treatment WL4 were zero and values for all water levels were within the theoretical range of 0 to 1.0. CWSI and ST were linearly related with yield.