What is VPD?
Vapour Pressure Deficit (VPD) is the difference between the amount of moisture in the air and how much moisture the air can hold when it is saturated.
Why is VPD important?
VPD is key to irrigation management decisions as it provides an indicator of how much irrigation is required to satisfy plant water loss. VPD can also be an indicator of plant stress.
Vapour Pressure Deficit (VPD) is the difference between the amount of moisture in the air and how much moisture the air can hold when it is saturated.
Why is VPD important?
VPD is key to irrigation management decisions as it provides an indicator of how much irrigation is required to satisfy plant water loss. VPD can also be an indicator of plant stress.
- When VPD is low this means the air has a low capacity to hold water because it is near saturation. ie: Low VPD = High humidity = Low evaporation potential. When VPD is too low, plants are unable to evaporate enough water, which can block the transport of minerals from the roots to the growing plant cells.
- When the VPD is high this means the air has a high capacity to hold water. ie: High VPD = Low humidity = High evaporation potential. When VPD is too high, the evaporation may cause the leaf stomata to close, halting photosynthesis in the plant, and the excessive heat in the plant can cause injury.
This chart illustrates the relationship of relative humidity and air temperature with VPD
(Adapted from Argus Ltd 2009).
How do we measure and summarise VPD?
VPD calculations are based on Temperature and Relative Humidity. The actual calculation is:
VPD in kPa = ((100-RELATIVE HUMIDITY)/100)*(610.7*10^(7.5*AIR TEMPERATURE /(237.3+AIR TEMPERATURE)))/1000
VPD = Saturation vapour pressure - Actual vapour pressure. Where the value is expressed in kPa.
VPD can be calculated with data from
VPD calculations are based on Temperature and Relative Humidity. The actual calculation is:
VPD in kPa = ((100-RELATIVE HUMIDITY)/100)*(610.7*10^(7.5*AIR TEMPERATURE /(237.3+AIR TEMPERATURE)))/1000
VPD = Saturation vapour pressure - Actual vapour pressure. Where the value is expressed in kPa.
VPD can be calculated with data from
- Any microclimate sensing solution (MCSS) location with a Meter Atmos 14 or Decagon VP4 sensor attached, or
- Any gridded location.
What does this mean for users?
Users will be able to view the areas of their sites that are within the ideal humidity and temperature range to be irrigated, so they can avoid watering at times when the plant cannot absorb the water.
Can I set up notifications for VPD?
This is likely to be available in a future release.
Am I be able to view VPD in the Analytics portal?
Users will be able to view the areas of their sites that are within the ideal humidity and temperature range to be irrigated, so they can avoid watering at times when the plant cannot absorb the water.
Can I set up notifications for VPD?
This is likely to be available in a future release.
Am I be able to view VPD in the Analytics portal?
Yes, users can view VPD within their portal’s worksheet if they have this condition configured for their site(s).
What does it mean when the VPD value has an asterisk next to it?
If an asterisk is displayed next to a VPD value, then this indicates that the timeline is showing predicted data. A VPD value with no asterisk is based on observed data.
Tap on the VPD value to view a chart of all observed and predicted values for VPD for the current day when making decisions on when to start and stop irrigation.
What does it mean when the VPD value has an asterisk next to it?
If an asterisk is displayed next to a VPD value, then this indicates that the timeline is showing predicted data. A VPD value with no asterisk is based on observed data.
Tap on the VPD value to view a chart of all observed and predicted values for VPD for the current day when making decisions on when to start and stop irrigation.
Comments
0 comments
Please sign in to leave a comment.