Reducing cranberry heat stress and midday depression with evaporative cooling

A cultural practice for cooling cranberry plants and avoiding yield losses due to overheating is to turn on sprinkler irrigation for a few minutes when a critical temperature threshold is reached. The purpose of this study was to determine: (i) the critical leaf temperature to start irrigation for evaporative cooling in cranberry production, (ii) the combined effects of heat and water stress, and (iii) the beneficial effects of evaporative cooling through irrigation on field microclimate and plant physiology. The optimum temperature range for carbon dioxide (CO2) assimilation was between 25 and 29 °C, with photosynthesis (An) declining by 11% at 33 °C and by 22% at 37 °C due in part to stomatal limitations. The reduction in An was greater under low soil moisture conditions. When applying sprinkler irrigation in the field, leaf temperature was reduced by 5-10 °C and the efficiency of evaporative cooling was greater, with greater vapor pressure deficit of the air within the crop canopy before the irrigation. Under controlled environmental conditions, one cooling event resulted in a carbon gain of 19% relative to untreated plants and was able to reduce midday depression. Additional cooling events during the day had no significant effect on carbon gain. Among the main cranberry-growing regions, New Jersey is an area where sprinkler irrigation for evaporative cooling could be beneficial for preventing yield limitations due to heat stress.