What is VPD? Vapor Pressure Deficit, VPD, is an indicator of the evaporation potential of water into the air. It’s a measurement that’s defined as the difference, or deficit, between pressure exerted by the moisture present in the air currently and the pressure at saturation. It’s one of several different methods that you can use to evaluate crop stress or water stress within a plant.
The VPD can be used to steer plants based on the concept that it affects the transpiration stream within the plants. When plants transpire, they’re not just pulling water and cooling themselves, they’re also pulling mineral nutrition from the water such as calcium and magnesium and transporting it through their xylem.
If you push the VPD in the sense that you want to drive the transpiration stream, then you want a lower humidity environment, and therefore a high VPD. What you’re effectively doing is driving minerals and water through the plant, causing cells to expand. You can also manipulate the temperature in addition to the humidity. That’s where VPD is useful because temperature can greatly affect a plant’s metabolism, nutrient uptake and more.
You can identify conditions that are going to influence how your plant acts. If you’re paying attention to your VPD, you can tie it to your plant responses. You can see how your plants will react in the environment. You can also learn how much water your plants are using throughout the day. It’s an indicator value that can approximate your plants’ stress responses.
You can also observe lots of different effects on the plants. You can see how the environment changes over the course of the day and what kinds of responses your plants give.
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