What is Plant Empowerment
Plant empowerment, often referred to as “Next Generation Growing”, is an integrated approach to cultivation, developed in the Netherlands. This approach prioritizes the plants, providing them with the best conditions to optimize photosynthesis, in turn maximizing plant growth and health.
Growing with plant empowerment is data-driven, utilizing sensors and plant measurements in combination with knowledge of plant physiology and physics.
Plant empowerment relies on the ability to monitor the greenhouse climate as accurately as possible, including:
- Air temperature
- Leaf temperature
- Relative Humidity
- CO2 concentration
- PAR light (photosynthetic active radiation)
Plant Empowerment Balances
To grow with plant empowerment, growers need to maintain 6 critical balances, 3 for the plant and 3 for the greenhouse:
When it comes to plants, the 2 forms of energy discussed are radiation and heat.
Plants don’t generate their own heat, making them dependent on external factors to regulate their temperature. An imbalance of energy inputs and outputs would cause an increase or decrease in temperature.
Plant empowerment emphasizes the radiation to temperature ratio (RTR) as a driving factor behind plant growth and well-being.
The water balance in the plant refers to root uptake as the input and evaporation, or transpiration, as the output. Keeping this equilibrium is critical to ensure the plant remains active and productive.
Assimilate balance (also referred to as carbohydrates or sugars)
Assimilates are the main building blocks for plant production. For plants to grow to their maximum potential, assimilate production needs to be maximized, while also ensuring consumption is optimized.
Reduced assimilate production would slow down growth, while excess assimilates in the plant are “wasted” on starch and cellulose production, which aren’t necessary in most cases.
The energy balance of the greenhouse is similar to that of the plant. An excess of inputs – solar radiation, heating and lighting will increase temperature. While an excess of outputs – heat emission, ventilation and convection will decrease temperature. Energy, in this case, is expressed in W/m2.
Outdoor conditions have a major impact on the greenhouse’s energy balance, as heat and radiation are constantly transferred.
The moisture balance is defined as the balance between inputs – evaporation from the plants, as well as misting in some greenhouse, and outputs – condensation and ventilation. Moisture, or humidity, is measured in relative humidity (RH), absolute humidity (AH) or vapor pressure deficit (VPD).
Maintaining this equilibrium is critical in stimulating the plant’s water uptake and transpiration.
CO2 is a crucial element for assimilate production. There are 3 major inputs of CO2 in a greenhouse – from outdoors, through enrichment and released by the plants through dissimilation. The outputs are defined as the plant’s CO2 uptake as well as CO2 lost to the environment through ventilation.
A greenhouse’s CO2 balance is greatly affected by the outdoors, as it can act both as an input or an output. If the CO2 concentration is higher inside the greenhouse, ventilation will decrease its presence and vice versa.
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Of course, all of these balances are interrelated and affect one another. Maintaining equilibrium is difficult, requiring all factors to be in balance in order to achieve optimal conditions.
How to Implement Plant Empowerment
Plant empowerment is about optimizing production. The basis of plant growth is photosynthesis – turning CO2 and water into assimilates and oxygen.
To optimize photosynthesis, growers need to maximize their PAR light, while supporting the plant by keeping its water and energy balances in equilibrium. This includes providing high levels of CO2 and high temperatures to increase the rate of photosynthesis, as well as maintaining a relative humidity that allows stomata to remain open and transpire. Optimal levels depend on the specific crop and may vary.
There are 5 simple steps growers can take to start growing with plant empowerment:
- Create climate uniformity
- Reduce heat emissions from plants
- Maintain greenhouse moisture balance
- Balance assimilates and radiation/temperature ratio (RTR)
- Maintain plant water balance
It’s important to note that data is at the core of plant empowerment. Monitoring the plants and greenhouse as precisely as possible is what allows growers to make the best decisions.
Create climate uniformity
Climate uniformity means maintaining the same conditions (temperature, humidity, CO2, etc.) throughout the entire greenhouse. This is the glue that binds together all other efforts. Without uniformity, it would be impossible to optimize the growth of all plants at once.
The most basic step to take, is to ensure the space is completely closed. Any opening leads to an exchange of air and reduces control over the greenhouse climate. Fixing leaks and sealing gaps can go a long way in increasing control and reducing unnecessary energy use.
Using thermal, shade or blackout screens helps prevent heat transfer and retains the heat found inside the greenhouse. This gives growers greater control over temperature and radiation, while decreasing fluctuations in the space.
Creating climate uniformity can be done with the use of air circulation. Ensuring heating and dehumidification efforts reach all corners of the greenhouse with the same intensity ensures similar conditions for all plants.
Reduce heat emissions from plants
Reducing the heat emissions from plants means maintaining their temperature. Higher plant temperature assists in “activating” the plant – increasing its photosynthesis and assimilate production.
Maintaining higher leaf temperature also reduces the chance of condensation on the plants, which would decrease its ability to transpire, inhibiting its growth. Condensation occurring on the plants also leads to disease outbreaks such as botrytis or powdery mildew.
Plant heat emission is directly influenced by greenhouse roof temperature. Lower roof temperatures would cause the plant to emit more heat. So, the most effective way to reduce heat emissions is by using a thermal screen.
Overnight, screens should be fully deployed, to retain the heat inside. In the early morning, while most growers would retract the screen to receive more sunlight, growers using plant empowerment may prefer to keep the screens spread until roof temperatures rise. Similarly, closing the screens afternoon (before sunset) will reduce heat emissions overnight, as the greenhouse roof temperature starts dropping before the sun sets.
Screening based on heat emission is different from traditional screening. While there are some downsides to this, there are greater benefits. Of course, this must be taken into consideration with other factors, such as lighting, heating and humidity control.
Maintain greenhouse moisture balance
Maintaining a greenhouse’s moisture balance is crucial. If the air is too dry, plants will go into water stress, cutting all transpiration and photosynthesis. When the air is too saturated with water vapor, plants won’t be able to transpire either. If the air becomes completely saturated, meaning relative humidity reaches 100%, water will begin to condense, resulting in molds and diseases.
To optimally stimulate plant activity, growers should maintain a VPD level of 1.2-1.5 kPa.
Growers using plant empowerment should monitor absolute humidity (AH), as well as the more common relative humidity (RH) and VPD. This is due to the fact that RH is affected by temperature, while AH isn’t, giving a better indication of the greenhouse’s moisture balance.
Energy (heat and radiation) increases evaporation, which increases moisture in the greenhouse. A good way to reduce evaporation is by decreasing these energy inputs, while still keeping them in optimal range. For example, excessive heating overnight will result in greater evaporation, increasing absolute humidity (AH). This may be counterintuitive, as heating decreases relative humidity (RH).
The best way to control the moisture balance in a greenhouse is with the use of dehumidifiers.
Ventilation is traditionally the main method of greenhouse humidity control. But ventilation requires optimal outdoor conditions. During cold or humid periods, such as overnight, during winter, or on rainy or humid days, ventilation may not assist in reducing humidity, and may even have an inverse effect.
Using dehumidifiers is the best way to control humidity during these periods. However, when it’s possible, growers should vent, rather than dehumidify, in order to reduce energy consumption.
Balance assimilates and radiation/temperature ratio (RTR)
Maximizing assimilate production is key to maximizing plant development and growth. But in order to achieve the best results, assimilate consumption must be matched with production.
Focusing on the production side, growers should maximize the sum of PAR light, as well as CO2 concentration.
As assimilate production is rather straightforward, plant empowerment focuses more on increasing consumption, to match production.
The consumption of assimilates depends mainly on the daily average temperature. A higher average will increase the consumption.
In fact, the best way to match consumption with production is by maintaining a balanced radiation/temperature ratio (RTR). This means that on brighter days, the average daily temperature should be higher.
Growers growing with plant empowerment will increase nighttime temperatures after brighter days. This lets the plant transport and process assimilates more effectively. Darker days mean less assimilate production, allowing growers to maintain lower temperatures overnight without creating assimilate excess in the plants.
Maintain plant water balance
Plant transpiration is extremely important, directly affecting photosynthesis as well as nutrient intake. Many growers prefer to control their greenhouse climate based on humidity, rather than temperature.
There are 2 main inhibiting factors when it comes to transpiration.
First, the relative humidity must be in optimal range. Too low and plants will close their stomata, resulting in no evaporation. Too high and the air becomes saturated, also resulting in no evaporation.
Second, there must be air movement. Stagnant air will cause relative humidity around the plant to reach 100%. Air movement dissipates the pocket of air around the plant, allowing it to keep transpiring.
As previously mentioned, although ventilation may assist in many situations, using dehumidification is the only way to ensure an active climate all day, year-round.
The Benefits of Plant Empowerment
Growing with plant empowerment has many benefits, for growers as well as plants.
Benefits to the plant
By providing plants the optimal conditions, keeping their balances in check, they can optimize their photosynthesis. This lets them maximize their assimilate production – the building blocks for the plant to develop. Growing with plant empowerment can also help achieve a steady growth balance (vegetative and generative).
Maintaining these balances reduces the plants’ stress, leading to more efficient growth – faster, larger and stronger. This also reduces the need for additional chemicals for fertilization or even pesticides. Stronger, healthier plants are less susceptible to diseases.
Energy and economic benefits
Plant empowerment prioritizes the plant, but one of its greatest benefits has to do with energy efficiency.
While traditional approaches to growing are based on assumptions and rules of thumb, plant empowerment is based on knowledge of physics, plant physiology, measurements and monitoring. Traditional approaches focus on individual factors, while plant empowerment focuses on balances between different factors.
For example, growers often strive to maintain a certain temperature range, without factoring in the amount of PAR light the plants receive. Plant empowerment takes them both into consideration, aiming for a balance, rather than individual values. Knowledgeable growers would therefore focus on the radiation/temperature ratio (RTR), which has a greater impact on plant development than temperature or radiation alone.
By understanding plant physiology and focusing on the plant’s needs, growers can shift climate conditions as necessary. While a traditional approach would be less precise and much more wasteful.
Another example would be the deployment of thermal screens. More traditional growers may deploy the screen when the sun sets, to maximize the sunlight. However, a grower growing with plant empowerment may choose to deploy the screen earlier, before the temperature outdoors start to drop. This would retain more heat overnight, resulting in better growth as well as reduced heating bills.
With plant empowerment, it’s all about understanding the interplay and balance between different factors, in order to make the most efficient decision.
This article is based on the book “Plant Empowerment – The Basic Principles”. Written by ir. P.A.M. Geelen, ir. J.O. Voogt and ing. P.A. van Weel, published by LetsGrow.