Managing Vapor Pressure Deficit in Greenhouses
(book excerpts)Vapor pressure deficit (VPD) is a more accurate way to measure greenhouse climate when determining water loss from the plant. Vapor pressure deficit is simply the difference between the vapor pressure inside the leaf compared to the vapor pressure of the greenhouse air. If the VPD is high (low humidity), meaning that the vapor pressure inside the plant is higher than the outside air, then more water vapor escapes out through the stomates (pores in the bottom of leaves). This process of water loss through the leaves is called transpiration. If the VPD is low (high humidity), the stomatal openings close, and little water and fertilizer are taken up by the plant from the growing medium. Vapor pressure deficit is important to know because it is used to schedule irrigations and to determine if air exchanges are needed and if air temperature needs to be increased in order to hold more moisture. Vapor pressure deficit is typically integrated into many greenhouses’ environmental control systems to manage humidity and for scheduling crop irrigation.
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Topics Within This Chapter:
- Relative Humidty
- Dew Point Temperature
- Role of Humidity in Plant Growth and Development
- Vapor Pressure Deficit
- Vapor Pressure Deficit and Plant Transpiration
- Vapor Pressure Deficit and Plant Stress
- Optimum Vapor Pressure Deficit Values
- Measuring Vapor Pressure Deficit
- Vapor Pressure Deficit Control
- Controlling High VPD
- Controlling Low VPD
