Developing a Cranberry Water Stress Index.

The crop water stress index (CWSI), based on canopy temperature is the most commonly used index to detect plant water stress. However, no such index has been developed for the American cranberry (Vaccinium macrocarpon Ait.). An experiment was conducted on five commercial cranberry beds to measure plant canopy temperature using infrared thermometers, air temperature, relative humidity and other weather related measurements, soil moisture content, soil moisture tension and plant response to water stress. The objective of this project was to develop a CWSI for cranberry plants. Linear regression techniques were used to develop a relationship between plant canopy and air temperature differences with vapor pressure deficit (VPD). Cranberry beds constructed on sand sub-grades were associated with higher stress levels compared with peat based beds. The matric tension of the soil increased with CWSI. There was a diurnal variation in CWSI with the highest levels of stress experienced between 1200 to 1500 hr in both sand and peat beds. Peat based beds had a highest CWSI of 0.4 while sand based beds reached CWSI of 0.9, indicating severely stressed cranberry vines. The CWSI can be a useful tool in making decisions on when to irrigate plants, but based on this data set, its usefulness is limited to clear and sunny days.