What is Vapour Pressure Deficit and How Does It Influence Plant Growth?

VPD stands for Vapour Pressure Deficit, which is a measure of the difference between the amount of moisture in the air and the maximum amount of moisture the air can hold when it is saturated at a specific temperature. VPD is a crucial factor in plant growth because it affects the rate at which plants can transpire and take up water and nutrients.

VPD can be used to influence plant growth by manipulating the environmental conditions to optimize the VPD levels for specific plants. Here's how it works:

Understanding VPD: VPD is determined by the temperature and relative humidity of the air. As the temperature increases, the air can hold more moisture, and the VPD increases. Conversely, as the relative humidity increases, the air holds more moisture, and the VPD decreases.
Ideal VPD Range: Different plants have different optimal VPD ranges for growth. By understanding the VPD requirements of a specific plant, you can adjust the environmental conditions to keep the VPD within the desired range.
Controlling VPD: To control VPD, you can manipulate either temperature or relative humidity. Here are some general guidelines:
    • If the VPD is too low: Increase the temperature or decrease the relative humidity to raise the VPD.
    • If the VPD is too high: Decrease the temperature or increase the relative humidity to lower the VPD.
Benefits of Manipulating VPD: Maintaining an optimal VPD range provides several benefits for plant growth:
    • Enhanced transpiration: Optimal VPD promotes efficient transpiration, allowing plants to take up water and nutrients more effectively.
    • Prevention of diseases: Maintaining the right VPD range helps control humidity levels, reducing the risk of fungal diseases.
    • Improved nutrient uptake: Optimal VPD encourages the opening of stomata, the tiny openings on the plant's leaves, facilitating nutrient absorption.
Monitoring VPD: VPD can be measured using specialized instruments like VPD sensors, or calculated using environmental data such as temperature and relative humidity. By regularly monitoring VPD levels, you can make adjustments to maintain the desired range.

    It is worth noting that VPD is just one factor among many that influence plant growth. Other factors like light, nutrient availability, and carbon dioxide levels also play important roles. Therefore, it is essential to consider VPD in conjunction with other environmental parameters when optimizing plant growth conditions.

    Ideal VPD for Crop Lifecycle

    Adjusting VPD to suit different stages of crop development involves understanding the VPD requirements of plants at each stage and manipulating the environmental conditions accordingly.

    Here is a general guideline for adjusting VPD throughout crop development:

    Germination and Seedling Stage - During the early stages of crop development, it is important to provide a favourable environment for seed germination and seedling establishment.
      • Maintain low VPD 0.6-0.8: Keep the relative humidity high (around 70-80%) to prevent excessive water loss from the seeds and seedlings.
      • Provide gentle air circulation: Ensure gentle air movement to avoid stagnant air around the seedlings, which can lead to disease issues.
    Vegetative Growth Stage - In this stage, plants focus on establishing a strong root system and growing leaves.
      • Moderate VPD range: Aim for a moderate VPD range (around 0.8-1.2 kPa) to promote transpiration and nutrient uptake without excessive stress.
      • Balanced temperature and humidity: Maintain a balance between temperature and relative humidity to achieve the target VPD range.
    Flowering and Fruit Development Stage - During this stage, plants allocate more energy towards flower and fruit production.
      • High VPD range: During the flowering stage of growth plants are mature, robust and capable of handling increased atmospheric pressure (1.2kPa-1.5 kPa)
      • Increasing the VPD during flowering will increase the rate of transpiration, and therefore nutrient uptake thus assisting the plant to produce the maximum possible yield.
      • Developing floral structures are vulnerable to attack by fungal and bacterial spores, therefore it is desirable to reduce humidity levels to 40-50% and minimise the chance of spore germination.

      In conclusion, Vapour Pressure Deficit (VPD) is a critical factor influencing plant growth, as it directly affects transpiration and therefore nutrient uptake in plants. By understanding VPD and its relationship with temperature and relative humidity, growers can optimize environmental conditions to suit specific plant needs. Maintaining an ideal VPD range offers numerous benefits, including enhanced transpiration, disease prevention, and improved nutrient absorption. VPD can be controlled by adjusting temperature and relative humidity, and it should be monitored regularly using specialized instruments or calculated from environmental data. Adjusting VPD throughout different stages of crop development allows for tailored environments that support germination, vegetative growth, and flowering and fruit development stages. Implementing these guidelines, growers can foster healthier and more productive plants, ultimately leading to improved crop yields.