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How Humidity Control Improves Nutrient Transport in Plants

There are many factors that affect plants’ ability to take in nutrients and spread them to the cells within the plant. One of the most effective ways to improve nutrient transport is humidity control.

What Is Nutrient Transport?

Plants are living organisms. Like any living being, they break down nutrients in order to grow and develop. But unlike other organisms, plants don’t eat. Rather, they get most of their nutrients from the soil, through the water they take in from their roots.

To simplify, plants are comprised of pipes. Water, which contains the necessary organic compounds, travels throughout the plant, from the roots, all the way to the leaves. The leaves then transpire the water to the air. This process seems to defy gravity. So how do plants do it?

First, we need to understand water. Water has unique physical properties. It’s comprised of hydrogen and oxygen atoms, connected by what’s called a hydrogen bond. This bond is what connects water molecules to each other, turning them into one body of water. So, when water starts flowing, the rest of it follows, creating a cohesive flow, even upwards.

Xylem and the Force Behind Plant Nutrition

Inside the plant, water flows in hollow tubes, known as xylem. But to flow upwards, it needs an initial force to start the process.

The initial tension is created in the stomata found in the leaves. When stomata are open, water evaporates to the air. If evaporation were to stop, the xylem pull would cease, the plant would stop transporting nutrient-rich water, and the roots wouldn’t take any more in. This would stop plant development, leading to slower growth, or no growth at all. Of course, this has a negative impact on the size and quality of crops.

So, transpiration is the key to plant growth.

There two main factors that affect the plants’ ability to transpire:

  • Sunlight or grow lights – stomata open in response to light, which allows water to evaporate. However, it’s important to note that some water still evaporates overnight, even in the dark, due to the plants’ respiration process.
  • Relative humidity – humidity has a direct impact on the rate at which plants transpire. Generally, higher humidity will slow down transpiration and lower humidity will speed it up. But if relative humidity is too low, or too high, nutrient transport will slow down or stop completely. It’s all about maintaining a proper balance.

How Relative Humidity Affects Nutrient Transport

Relative humidity measures the amount of water vapor in the air, as a percentage of how much water the air can hold. So, 100% relative humidity means the air is completely saturated and can’t hold any more water.

In order for plants to transpire, the air surrounding them (the boundary layer) must be able to take in more water vapor. If the air has already reached the dew point, as in 100% saturation, there is no where for the water vapor to go. In this case, water will simply cease to evaporate, halting the xylem pull and stopping nutrient transport in the plant.

So, to properly develop, plants require relative humidity levels comfortably under 100%.

But extremely low humidity has its problems as well. When the air is too dry, water evaporates at a rapid rate. So, to protect themselves from extreme water loss, plants enter a state of stress, in which they close their stomata in an attempt to retain water. When plants close their stomata, they barely transpire, leading to similar results as high humidity.

For most plants, 60%-80% relative humidity is considered an optimal range.

How to Use Humidity Control to Improve Nutrient Transport

Controlling humidity is one of the most effective ways to improve nutrient transport, increasing yields and improving quality.

Traditionally, greenhouse growers use a combination of heating and ventilation to control humidity.
Temperature directly affects the air’s ability to hold water vapor. Hotter air can hold more water than colder air, so heating does reduce relative humidity. But it doesn’t actually remove water vapor from the greenhouse, so once temperatures drop, relative humidity will spike. To combat this, growers ventilate as well, releasing the humid air from the greenhouse.

The problem with heating and ventilating is that hot air is also released in the process, which then requires more heating. Not only is this method inefficient and wasteful, but it’s also ineffective under various circumstances, such as rainy weather, humid or cold days and during most nights.

The only way to fully control humidity without wasting energy is by using dehumidifiers. This way, you can keep the greenhouse completely closed, retaining heat, while physically removing water vapor from the air.

Using a dehumidifier in a closed space has several benefits, other than efficient humidity control. By decoupling temperature and humidity control, growers gain more control over their greenhouse climate. Being able to adjust temperature and humidity separately ensures optimal climate conditions, with minimal energy requirements.

Closing the greenhouse, preferably with the use of screens, also drastically reduces pest and disease outbreaks and allows full control over lighting. All of these contribute to higher quality crops and larger yields.

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