Humidity in Dubai: How It Affects Farming

Everything in an environment affects the growth of a plant, from how it thrives, to how it reproduces. When you plan to grow plants indoors, especially in UAE, climate control is essential to maximize the photosynthetic process. You must ensure plant transpiration by maintaining optimal relative humidity levels in a greenhouse and other growing environments.

Humidity in Dubai – How It Affects the Plants

Relative humidity is the amount of water vapor in the air relative to the maximum amount of water vapor air can hold at specific temperature. Consequently, if the relative humidity level is 75% at 80° F, every kilogram of the air in the respective space contains 75% of the maximum amount of water it can hold for the given temperature.

The relative humidity levels affect when and how plants open the stomata on the undersides of their leaves. Plants use stomata to transpire or “breathe.” A plant may close its stomata in warm weather to decrease water losses. The stomata act as a cooling mechanism.

When environmental conditions are too warm for a plant, it closes its stomata for too long to conserve water. It does not have a way to move oxygen and carbon dioxide molecules, and it will slowly cause the plant to suffocate on water vapor and its own transpired gases and eventually die.

As a plant transpires, the humidity around saturates leaves with water vapor. When the relative humidity levels are very high, or there is a shortage of air circulation, a plant cannot make water evaporate. Neither can it draw plant soil nutrients. When this occurs for a more extended period, a plant eventually rots. A plant’s transpiration rates increase when surrounded by warm temperatures with low relative humidity levels.  

Humidity in Dubai-Importance of Climate Control

As seedlings grow or when you propagate plants from leaf or stem cuttings, the young or collected plants close their stomata as a protective measure to prevent water loss. To support cuttings and young plants, farmers usually use propagation chambers or plastic tents that increase the relative humidity levels surrounding the leaves and ensure proper circulation.

In addition to air and water, plants use light energy for transpiration. Light causes liquid water to convert to vapor as evaporation. Greenhouses usually maintain relative humidity levels below threshold values for day and night. This is done by controlling the water content in the air to maintain a minimum plant transpiration rate.

Climate control for plant growth is essential regarding disease and pest management. When the conditions are too humid, it can promote the growth of bacteria and mold that can cause the rotting of plants and eventually lead to their death. Humid conditions also lead to the presence of pests, such as fungus gnats, whose larvae feed on the roots of the plant and thrive in moist soil. Soil profile and soil fertility too plays an important role.

Humidity in Dubai – Why is it So Important

Humidity can be the most challenging environmental factor to control in greenhouses. Even the most sophisticated ecological control equipment cannot perfectly maintain the humidity level in greenhouses. The levels of humidity fluctuate with changes in air temperature, and plants constantly transpire, adding water vapor to the air.

In the northern climatic areas, these challenges get multiplied by many factors. It also includes the drier, outdoor air that is too cold to perform air exchanges.

Humid air directly adds to the problems such as root and foliar diseases, plant stress, slow drying of the growing medium, loss of quality, loss of yields, and many more. Consequently, more pesticides are required for disease control. Eventually, the plants tend to have weak, stretched growth, making the plant less desirable.

If the humidity is very low, plant growth is often compromised as crops take much longer to obtain the saleable size. Also, lower leaves often drop off. Change is complex and has poor overall quality.

Whether the humidity is very high or very low, the loss of quality reduces the selling price of crops and increases production costs. Consequently, both these factors ultimately minimize profit.

Humidity in Dubai – How to Measure Water Loss From the Plant

The maximum amount of water vapor that can be held by the atmosphere is dependent on the air temperature (warmer air has more water than colder air) and, to a lesser extent, the air pressure. When referring to air moisture, we usually express it in relative Humidity (RH).

The absolute amount of water that air can hold constantly fluctuates with temperature. Relative humidity is the most common way of expressing humidity levels but does not reveal plant water loss.

Vapor pressure deficit (VPD) is more accurate when determining water loss from the plant. VPD is the difference between the vapor pressure inside the leaf and the air’s vapor pressure. If the VPD is high, the vapor pressure inside the plant is higher than the outside air.

The higher value of VPD means more water vapor escapes through the stomata. This process of water loss through the leaves is transpiration. If the value of VPD is low, the stomata openings close, and the plant takes up little water and fertilizer.

VPD is essential because it is used to schedule irrigations. Additionally, it determines whether air exchanges are needed and whether the air temperature needs to be increased to hold more moisture.

VPD has been integrated into several greenhouse environmental control systems to manage humidity and schedule crop irrigation.

Humidity in Dubai – Role of Humidity in Plant Growth

Plants are constantly adjusting their leaf stomata openings based on the Humidity and VPD in the air. Higher Humidity is a problem because water usage by the plant is too slow and compromises quality, even though the stomata remain open.

On the other hand, if the Humidity level is significantly less and subsequent transpiration is too high, the plant closes its stomata openings to minimize water loss and wilting. Consequently, this also means photosynthesis process slows down plant growth.

As mentioned above, transpiration and photosynthesis are two primary functions of the plant that are heavily dependent on the Humidity in the air and affect crop performance.

Humidity in Dubai -Transpiration and Photosynthesis

The Plant Transpiration Process

Transpiration is the process in which plants absorb water through the roots and release water vapor through pores located in the leaves. The drier or hotter the air temperature, the faster the plant’s transpiration rate will be. However, the moisture deficit and transpiration rate are not related directly.

This means that the increased rate of transpiration in dry air can only go so high in the plant that it begins to wilt. For example, if the air is dry but the growing medium has enough water, the plant may wilt, and unless the Humidity increases, the plant could die.

On the other hand, if the air is very humid, the plant does not take up much water from the growing medium, which means there is little uptake of fertilizer elements. This is a problem for some elements, particularly calcium, as inadequate uptake can lead to nutrient deficiencies.

Also, low water usage from the growing medium often correlates with climbing growing medium pH, making micronutrients such as iron unavailable to the plant. 

The Photosynthesis Process

When the temperature is high, and higher humidity levels are expected, more stomata will open. The large number of open stomata will let in carbon dioxide for active photosynthesis. If the air is arid and the plant is wilting, the stomatal openings close, reducing photosynthetic activity and, ultimately, plant growth.

The crop’s quality depends on the conditions that promote optimal photosynthesis, and Humidity plays a role in this process.

Humidity in Dubai – Reduce Humidity in Greenhouse

It’s essential to maintain a certain level of Humidity in the greenhouse. It must not reach to the point where it reaches the dew point. If the temperature in the greenhouse is at or below the dew point, the air cannot hold its moisture and starts to condense on the greenhouse, covering glazing and leaf surfaces. Water on leaves significantly increases disease problems and minimizes water uptake by the plant, growing nutritional issues.

Sometimes it is challenging to keep the temperature above the dew point. The air in the greenhouse becomes very humid during winter when air exchanges are limited. It is also a challenge as the greenhouse glazing is often cold due to frigid outside air. Thus, the moisture in the warm, humid internal air will condense inside the glazing.

Dripping becomes a significant concern, as it causes uneven crop drying and increases diseases. Using air flow devices and heating the air dramatically helps. However, relative humidity can still be high enough to form condensation on cold surfaces.

Infrared radiant heating system can help reduce condensation. It can raise the temperature of hard surfaces, like plant and growing media surfaces. However, it cannot do so for  air, so there is minor temperature variation between the inside and outside air. You can keep the air temperature uniform throughout the greenhouse by using fans and thermal screens.

Avoid sudden temperature fluctuations. You can also adjust irrigation practices based on the greenhouse environment and weather. All of the above are excellent methods to manage Humidity and reduce condensation in the greenhouse.

Bottom Line

Managing the growth and development of plants involves the manipulation of a growing environment. These factors are light, temperature, and relative humidity levels. This promotes photosynthesis, high yields, and generative growth. Optimal transpiration rates vary by plant type, age, and season, making climate control for plant growth necessary throughout the year.

Al Ardh Alkhadra can offer custom-made temporary climate control solutions that create the ideal growing environment. You can do this by regulating and monitoring temperatures and humidity levels.