Controlled Environment Agriculture Webinar Series

 Dr. Fadi Al-Daoud, OMAFRA's Greenhouse Vegetable Specialist, will be hosting a webinar series focused on Controlled Environment Agriculture (CEA). This will cover information relevant to all  protected crops, including berries, vegetables and floriculture. 

Join Fadi, and his guest speaker Peter Kamp, in the first installment of this webinar series on January 20, 2022 at 1 pm AST. Peter will be discussing a new crop steering principle which hinge on the basis of overall water balance within a plant. 

For those of you who are not familiar with the concept of plant steering, it operates on the basis of manipulating environmental factors to encourage vegetative or generative growth. Both vegetative and generative growth are important for establishing a healthy crop, but it is important that the timing of these two stages happens at specific time points during the cropping cycle. There are a handful of ways  we can push a crop towards increasingly vegetative growth, or increasingly generative growth, and this webinar looks to discuss a new tool to be added to our steering toolbox. For more information on crop steering, check out three of our previous posts titled 'Creating a Balance'. Each has been tagged with the tagline 'vegetative' and 'generative', so scroll through our tag list on the right side of your screen to take a look!

For anyone interested in registering for the session, click here for the link. 

Hope you there!

Posted by: Talia Plaskett

Creating a Balance - Vegetative vs Generative Growth

Part 3 - Tampering with Temperature

So far, we have explored the differences between vegetative and generative growth, and the role that water availability and EC play in steering the crop in either direction. Now it is time to explore the impact that temperature and humidity have on these two types of growth.

• Water availability
• EC
• Day/Night temperatures
• Vapour Pressure Deficit (VPD)
•  Pruning
•  Fruit load

Day/Night temps

While we are accustomed to focusing on the temperatures through the day, it is also important to consider the greenhouse temperature at night. With a high night temperature, you are going to see higher rates of respiration, which results in a decreased fruit weight. Allowing the space to cool down over the night is a good strategy to maximize yield. Be careful here though, because too low of a night temperature will result in poor fruit quality.

Not only does a cooler night temperature (compared to the daytime temperature) reduce respiration in your fruit, but it also encourages generative tendencies in the plant. Holding your temperature steady over 24 hours puts the plant into a more vegetative growth pattern.

A good strategy for transitioning from you night temperature to your day temperature, is to allow the space to heat up 1-1.5 hours before sunrise. This is important in maintaining the shelf life of your crop once it has been harvested. Without this warm-up period, you will likely end up with condensation in the production space, which can lead to a variety of issues.

Like irrigation, these highs and lows should be modified on cloudy days – reducing that temperature gap when there is less sunlight will prevent the crop from becoming overly stressed.

Vapour Pressure Deficit (VPD)

Vapour pressure deficit (measured in kPa) compares the amount of moisture in the ambient air, to the amount of moisture in the air surrounding the plant. It is a driving force for transpiration and determines how quickly or slowly the moisture moves out of the plant.

High VPD

•      low moisture content in the ambient air
•       big difference in moisture content between the air and the plant
•      water is rapidly pulled from the plant leaves, putting pressure on the roots to transport more water

Low VPD

•        high moisture content in the ambient air
•         small difference in moisture content between the air and the plant
•         water is not pulled from the plant as quickly
•        more vegetative plant

How do I know where I stand?

The chart posted below can be used to help visualize the energy relationships of moist air. Based on your VPD reading and the temperature of the grow space, you can determine what the ideal humidity is (and vice versa). By maintaining a VPD in the target zone (shown in green in the chart below), you can rest assured that the air-water relations have been optimized within the plant and prevent encouragement towards vegetative production. Once you start steering towards the red zones on either side, an adjustment should be made to get back into the target zone. Fluctuation in temperature or humidity is okay if the appropriate adjustments are made to keep the system in balance.

Figure 1.  The above chart serves as a guideline for creating an ideal greenhouse environment. Taking regular VPD measurements, in addition to temperature and humidity, will help to keep the system in check. Table was sourced from https://scienceinhydroponics.com/2017/04/vapor-pressure-deficit-vpd-in-hydroponics.html

Posted by: Talia Plaskett

Creating a Balance : Vegetative vs Generative Growth

Part 2 - It's All in Your Water

There are many factors that play a role in managing vegetative and generative growth, and it is important to consider a well-rounded approach when attempting to swing the scales. Keeping a balanced growing environment is important for a highly productive plant and changing one thing and nothing else will end up causing more harm than good.

In part 1 of this mini-series, we addressed the need for vegetative growth to have a high yielding crop. Vegetative action is required early in the crop cycle so the plants can establish themselves. By creating this strong base, the plant will be able to support a highly productive generative state later on.

The generative growth phase focuses on managing plant productivity. It is achieved through strategic stress induction in your plants. These minor stresses are going to push the plant to divert resources to reproductive organs (fruits), while ensuring that all other plant processes can be maintained. The key word here is minor – pushing the plant too far is not going to have the response you are looking for.

How Do I Manipulate the Plant?

A few of the major contributing factors to vegetative and generative growth are listed here below. We will address the impact that each factor has on crop steering.

•        Water availability
•        EC
•        Day/Night temperatures
•        Vapour Pressure Deficit (VPD)
•        Pruning
•        Fruit load

Water Availability

Watering frequency, duration and timing plays a role in pushing the plant towards a more vegetative or generative state.

In vegetative action, water is readily available for the plant when it needs it. The plant does not have to work hard to uptake water and will readily create new above- and below-ground biomass. As roots and leaves are being produced, the plant is preparing for full-blown production. Higher water content in the substrate is achieved through small, frequent irrigation events throughout the day.

Once it is time to switch to generative growth, these watering events become longer and more infrequent. As water becomes less available, less energy is put towards the production of root and shoot material, and more will be diverted to fruit production. The plant will now have to actively seek water compared to it being readily available in the vegetative stage.

Figure 1. Depicted here is the general irrigation strategy for substrate-grown greenhouse crops (ex. Tomato). Water content (WC) is depicted in green. While the timing and frequency of watering for generative and vegetative phases will vary, the general concept applies. As the day ramps up, you slowly increase the amount of water you deliver to the crop. After you achieve first run-off, you can start hitting the crop with water at regular intervals (determined, in part, by the weather that day). As the end of the day approaches, irrigation stops all together. Photo credit: Greenhouse Canada, June 2010 (https://www.greenhousecanada.com/september-2010-2418/)

While the daytime irrigation strategy is important in crop steering, you must also consider what is happening through the night. The length of the dry-down period of your growing media will help to tip the scales towards vegetative or generative tendencies. A short dry-down period (usually achieved by scheduling the last irrigation event of the day 1-2 hours before sunset) encourages vegetative growth. A longer dry-down period (which would have the last irrigation event happening earlier in the day) will encourage generative tendencies.

EC Measurement

The electrical conductivity (EC) of your fertilizer solution is important to consider when encouraging vegetative or generative action. EC is an indication of the salt content in the solution and will therefore impact water availability to the plant. A higher EC value means a higher salt content, and the harder the plant must work to take up water. As the plant works harder to take up water, less resources will be sent to vegetative growth (leaves, roots) and more will be sent to the generative tissue.

Here is a rough guideline of where your target EC should be, based on the crop stage:

Plant Stage	Target EC
Germination (vegetative)	0 - 1
Plant raising (vegetative)	2.5 – 3
Harvesting (generative)	2.75 – 3.5*
Full harvest (generative)	2.75 – 4*

*Should be watering with an EC of around 3, but you will see a higher substrate EC as the salts accumulate in the grow media

Understanding how your watering habits sway the crop in one direction or the other is a good starting point. Irrigation is something that all protected producers have control over, and it is important to see that watering plays a huge role in plant phenology and overall production capacity.

Creating a system that encourages maximum production capacity is in everyone’s best interest, and it is extremely important that all factors are addressed when trying to push for a more generative crop. Adjusting the watering and EC alone are not going to be enough to hit the target yield. All plant processes are intertwined and should be carefully considered whenever adjustments are made.

Stay tuned for our next post on vegetative vs generative growth, which looks at the role of temperature and humidity in crop steering.

Posted by: Talia Plaskett

Creating a Balance: Vegetative vs Generative Growth

Part 1 - Setting the stage 

Most greenhouse vegetable producers will have come across vegetative versus generative growth in their vine crops (tomato, pepper, cucumber). Over the next few weeks, we will be exploring the differences between the two types of growth, what they look like, and how we can manipulate the plants to encourage one form of growth over the other. This information will be focused on tomato production, but it is important to note that the same concepts apply to other crops.

Vegetative growth is characterized by:

• Thick stems
• Lots of leaves and suckers
•  Leaves are long and can be twisted/curled
• Dense growing tip
• High density of leaves
• Small fruit
• Elongated fruit truss

The plant is putting most of its energy towards the production of plant material. While leaves are important for photosynthesis, tipping the balance towards a more vegetative state does not leave enough energy being diverted towards fruit production. The size and quality of the fruit coming off a vegetative plant will be significantly less than what you would want.

Figure 1. An image of an overly vegetative tomato plant. Notice the thickness of the stem, the high density of plant material, and the curling of the leaves. Photo credit: Government of Alberta, Tomato plant propagation in commercial greenhouse tomato production (https://www.alberta.ca/tomato-plant-propagation-in-commercial-greenhouse-tomato-production.aspx)

Generative growth is characterized by:

•       Thin stems
•       Fewer leaves, typically shorter in length
•       Good sized fruit
•       Slight purple tinge to the growing tip

These features indicate that the plant is putting most of its resources towards fruit production. While we want to see generative growth, it is possible to tip the balance too far. A plant that is overly generative, will not have the leaf resources available to power plant growth. Overly thin stems with few leaves will not be able to support a high fruit load, and the resulting fruit will not be of market quality.

 

Figure 2. A tomato plant that is growing generatively. Notice that the stem is significantly thinner here compared to Figure 1. The leaves are much less densely packed, and the leaves are not curling excessively. Photo credit: Talia Plaskett, Perennia.

Production of greenhouse crops requires both types of growth for optimum production. The act of rooting after transplant is considered vegetative. You want to encourage the plant to establish a good strong base in the growing media, so that it can support the plant through the growing season, and push for high yields. After a certain point, you want to start pushing the plants to a more generative state. This will encourage more fruit, and of a higher quality as well.

How do I know where I stand?

Designate one or more areas within the greenhouse as being your primary monitoring spot. This area should be representative of the growing conditions in that space – many growers will choose the centre of the tunnel/greenhouse, and pair this with the location where they are collecting information on drain EC/pH and slab weight. Each production space should be considered its own entity, as temperature, humidity, air circulation etc. will vary between bays despite our best efforts.

Within this monitoring block, a series of measurements should be taken weekly. Things like stem width (measured below the youngest flower cluster with an open flower), internode length, leaf length, weekly growth, and number of leaves/clusters will let you know how the crop is doing. Keeping this information on record will help you get an idea of how your interventions paid off, and generally how the crop is doing. These measurements can also be used to forecast future yields and therefore what will be available for retail.