1. What is Leaf VPD?

Vapor Pressure Deficit (VPD) is the difference between the amount of moisture in the air and how much moisture the air can hold when it's saturated. Leaf VPD specifically refers to the vapor pressure deficit at the leaf surface, which is crucial for plant transpiration and growth.

2. How Does the Calculator Work?

The calculator uses the simple VPD equation:

Where:

• \( e_s \) — Saturation vapor pressure (kPa)
• \( e_a \) — Actual vapor pressure (kPa)

Explanation: The equation calculates the difference between the maximum possible water vapor pressure (saturation) and the actual water vapor pressure in the air.

3. Importance of VPD Calculation

Details: VPD is critical for understanding plant water relations, managing greenhouse environments, and optimizing irrigation schedules. It affects transpiration rates and plant growth.

4. Using the Calculator

Tips: Enter both saturation vapor pressure (e_s) and actual vapor pressure (e_a) in kPa. Both values must be positive numbers, with e_s > e_a for meaningful results.

5. Frequently Asked Questions (FAQ)

Q1: What is a good VPD range for plants?
A: Optimal VPD ranges vary by plant species and growth stage, but generally 0.8-1.2 kPa is good for most plants during the day.

Q2: How do I measure e_s and e_a?
A: e_s can be calculated from temperature, while e_a can be measured directly with humidity sensors or calculated from relative humidity.

Q3: Why is VPD important in greenhouses?
A: VPD helps maintain optimal transpiration rates, preventing both water stress and excessive humidity that can lead to disease.

Q4: What happens when VPD is too high or too low?
A: High VPD causes excessive transpiration and potential wilting. Low VPD reduces transpiration and nutrient uptake, and can promote fungal growth.

Q5: Can VPD be negative?
A: No, by definition VPD cannot be negative as e_a cannot exceed e_s.