A Thermal Stress Index for Cotton
- J. J. Burke ,
- J. L. Hatfield and
- D. F. Wanjura
Thermal stress is difficult to separate from water stress; however, linking enzyme kinetics to plant temperature provides a new description of plant stress. Previous reports have shown that cotton was within its thermal kinetic window (the temperature range over which the value of the apparent Michaelis constant (Km) of enzymes remains within 200% of the minimum observed value) for approximately 30% of the growing season, and that the time the plant temperatures were within the thermal kinetic window (TKW) was related to biomass production. The present study investigated the usefulness of the 27.5 °C midpoint temperature of the TKW of cotton (Gossypium hirsutum L.) as a baseline temperature for a thermal stress index (757). Using this biochemical baseline and measurements of foliage temperature, we compared the TSI response with cotton field performance. The study was conducted in the field on an Olton silty clay loam soil (fine mixed, thermic, Aridic PaleustoIIs) during 1984 and 1987. Measurements of foliage temperature were made with a hand-held 4° field of view (FOV) infrared thermometer and plant biomass measured by destructive sampling. The biochemically based TSI and the physically based crop water stress index (CWSI) were highly correlated (r2 = 0.92) for cotton across a range of environmental conditions. The results indicate that the TSI may be useful in quantifying thermal stress via a procedure related to plant biochemistry.
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