Plant Physiology

In order to maximize the yield, we need to know how to balance the vegetative-generative condition of plants. The highest possible amount of crop can only be harvested if the plants expend most of their energy into crop production. Every extremity, be it climatic, the alteration of soil moisture and/or that of the nutrient content or any other factor reduces the potential yield as when plants need to compensate for the negative effects of the extreme conditions they need to expend energy, which they possess only in limited amount.

Let’s aim at keeping the vegetative-generative balance.

How can we accomplish it?

Lets take the growing facilities without heating as an example (e.g. in Almeria, Spain). In case of these, the climate cannot or only partially can be controlled so managing the balance of the plants in these type of greenhouses with this device is not possible. Still, we need to be aware of the fact that the climate makes the plants move to the generative direction due to the excessive fluctuation in daytime and nighttime temperature and that of humidity in this kind of greenhouse environment.

To eliminate this, the use of our other two devices is needed.

Managing the mass of foliage – in case of plants where this technique is used, e.g. tomato, more intensive de-leafing is necessary (removing more leaves at the same time).

Irrigation, controlling the nutrient provision of plants – the growing medium needs to be kept wetter, high fluctuation needs to be avoided, it is recommended to water more often and possibly at a lower dose.

Drying out makes the plants move to the generative direction in two ways.

On one hand, when the water leaves (via evaporation from the growing medium) one part of the nutrients stay, increasing the salt concentration (EC) in the growing medium. If the deviation from the optimum goes to extremities, it produces stress in the plants and due to this the plants will expend their energy on their subsistence, reproduction, the growth of their offsprings, that is on crop production. This could be considered as a good thing, as everyone wants to have a good harvest, but unfortunately in case of an imbalance in the generative direction, the plants make do with lower crop production in order to ‘look after’ their seeds (offsprings), which leads to reduction in crop size as well as in the total weight of the harvested crop.

On the other hand, root hairs, which are active participants in the uptake of water and nutrients as part of the root system, always strive for finding the optimal water-air ratio in the growing medium (which is about 70-30%). This involves movement as root hairs grow where this optimum is at present. Should the place of the optimum change, as the given place dries out and the ratio of water decreases, or the ratio of air decreases due to over-irrigation, the roots move forward looking for the optimal condition.

The knowledge of plant physiology suggests that if a plant is lacking in the sufficient amount of energy, it first directs its available energy into the roots, then into the crop and only last of all into the foliage. Consequently, if the movement of the roots requires constant energy, there is less energy available for developing crop, which leads to less available yield.

Soilless cultivation presents further challenges to the growers, including the method of irrigation which is crucial to the successful production. Different growing media possess different water storage and rewetting abilities due to their density, their special compound, material and size.

Specialists agree that varieties with great genetic potential are unable to produce higher yield without a proper irrigation strategy. They are even less tolerant of failures in the plant management system. The proper dose of irrigation water and its usage are of great economic and environmental importance as well.

Plants need healthy and constantly renewable root system, as well as sufficient amount of oxygen in the growing medium. Furthermore, to reach the optimal level of growth, they need controlled change in the water content of the growing medium in accordance with the time of the day. The change of water content within the growing medium triggers vegetative or generative impulses in the plant. In order to keep the balance within the plants, extreme values might be needed in certain situations and this is impracticable without accurate and reliable control.

When do we need to start to irrigate?

The timing of the first morning watering has a great effect on the plants. The effect of irrigation on plants is primarily determined by the difference between the highest value of water content during the last watering of the previous day and the water content value of the first watering the following morning.

It is widely accepted that in order to maintain the balance of the growth rate this value should be targeted between 6% and 12% in acclimatized greenhouses.

These values may differ in both directions depending on the geographical and climatic conditions, as well as on the momentary state of the plant.

Depending on whether the plants need vegetative or generative impulses, we can decide on the targeted value of this difference. If we aim to move the plants in the vegetative direction, this value can be lowered, approximating the 6%.

If the aim is to move the plants in the generative direction, the targeted value of the difference should be higher, close to 12%.

A remarkable daytime-night-time fluctuation in temperature is highly probable to present itself in case of growing facilities where temperature (plant temperature) and humidity cannot be precisely controlled, especially during sunny periods. This is already a stressful situation for the plants, which provides them with a generative character.

Therefore, in such environment the fluctuation between the target values should possibly be kept low, between 2%-4%. Here, however, there is a strong emphasis on accurate measurement as plant management can already be affected by a difference as little as 0,5%.

In case of cloudy weather the difference in temperature will not be that significant. In such cases the higher value needs to be approximated.

As plants are exposed to different environmental effects day by day, their nighttime water uptake can also differ excessively, making the time-based start of irrigation highly hazardous.

The alarm function on the touchpad of the Trutina provides solution to this problem. We can set the value of this difference, given in percentage, at which we want to start the irrigation. When the water content of the growing medium reaches or exceeds this value the systems sends an alarm message, providing the ideal timing for the start of our first irrigation.

After having taken the first step by starting the first morning irrigation, our next aim is to reach the value of the maximum water content of the previous day and to keep the substrate moisture around this value during the day, possibly until the last irrigation of the day. An increased dose of water is usually chosen in order to reach the daily maximum water content quickly.

Having reached the desired maximum value, we have arrived at the third period of our irrigation strategy where we aim to maintain this maximum value by the desired 1-3% fluctuation of the water content in the growing medium between the different times of watering. The necessity of drain needs to be taken into consideration.

The optimal values may differ in both directions depending on the geographical and climatic conditions, as well as on the momentary state of the plant.

Important! Inappropriate choice in the dose of water or in the time period between each phase of watering may lead to unwanted increase or decrease in the water content.

In order to avoid the above situation, an alarm can be set on the touchpad of the Trutina to signal the values outside the given range, which makes it possible to react to the changes in circumstances.

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