Estimating the actual transpiration rate with compensated levels of accumulated radiation for the efficient irrigation of soilless cultures of paprika plants

• Actual relationship between light intensity and transpiration rate at an interval of 10 min was analyzed.
• A compensated equation that can calibrate the light intensity applicable to irrigation control was developed.
• Calibrated light intensity reduced water and nutrients without reduction in plant growth, especially in summer.
• A new irrigation method developed was efficient in terms of plant growth as well as water saving.

Water management directly affects the productivity of paprika plants and is currently determined based on accumulated radiation levels. However, the amount of water used by the plants, which can be determined by their transpiration rates, does not always increase proportionally to the accumulated radiation levels, depending on the region and climate as well as crop growth stages and development. This effect is observed because the transpiration rate is also related to light intensity, which varies with the time of day and season. To develop a more efficient irrigation strategy, both factors should be analyzed based on the relationship between light intensity and transpiration rate in the short-term. In this study, a sigmoidal relationship between light intensity and transpiration rate at an interval of 10 min was observed using a consecutive transpiration monitoring system. From this relationship, a compensated equation that can calibrate the light intensity was developed. When a modified irrigation was applied using this compensated equation, less water was used compared to a conventional irrigation that supplies water proportional to accumulated radiation, especially in summer. Moreover, there were no significant differences in the transpiration rates and plant growth between plants watered with either the conventional or modified with compensated equation irrigation method. From these results, it was concluded that water was used more efficiently with the modified irrigation method without affecting plant growth. In a region with a high solar radiation in summer, such as Korea, using our equation to calculate for light intensity can prevent water waste, resulting in energy-saving and a reduction of environmental pollution in open-loop soilless cultures.