To maximise tomato yield, growers need to know how to balance the vegetative – generative condition of their plants.
The highest possible yield is harvested when the plants expend most of their energy into crop production (fruit).
Every extremity, be it atmospheric, or fluctuations in root zone moisture &/or nutrient formula reduces the potential yield.
When plants compensate for the negative effects of extreme conditions they otherwise expend their limited energy.
Vegetative / Generative Balance
(Leaf / Flower Balance) EXAMPLE – Hot climates with no heating
When a hot climate cannot be controlled, or even only partially, it limits one’s ability to manage the plants’ balance.
Tomatoes will become more generative with excessive ﬂuctuations in day and night time temperature and humidity.
Control can be managed through;
- De-leafing the foliage
- Irrigation e.g. root zone moisture + nutrient control.
By watering more often with a lower nutrient dose the root zone stays wetter without fluctuations.
Otherwise, drying out the root zone encourages generative fruit production in two ways;
- Root zone evaporation increases salt concentration (EC).
- Plant stress from extreme deviation from the optimum climate makes them expend their remaining energy on subsistence such as their own reproduction, growth of offsprings, which is indeed crop production.
Quality and quantity are usually related and if you are not careful a generative imbalance can lead to lower yield in order to ‘look after’ the next generation.
Healthy Root Hairs
Root hairs perform at their best as active participants in the uptake of water and nutrients when the water-air ratio in the growing medium is about 70-30%.
If the root zone environment changes by either drying out or suffocating through over-watering, the plant sends energy to the roots to move and seek better conditions.
This takes away energy from the flowers and fruit.
Plant physiology suggests that if a plant is lacking in a sufficient amount of energy, it ﬁrst directs its available energy into the roots, then into the fruit 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.
Different growing media possess different water storage and re-wetting abilities due to their density, absorbency, material and size.
Specialists agree that a proper irrigation strategy can unlock a greater genetic potential and produce a higher yield.
The proper dose of irrigation nutrient is of great economic and environmental importance.
Plants need a healthy and constantly renewable root system, as well as a sufficient amount of oxygen in the growing medium.
They also enjoy different water content of the growing medium according to the time of the day.
The change of water content within the growing medium triggers vegetative or generative impulses in the plant.
To maintain plant balance accurate and reliable control enables sometimes extreme values, to steer the plant in the right direction of high yield.
When To Start Irrigating?
The timing of the ﬁrst morning watering has a great effect on the plants as well as the difference in salt content compared to the last watering on the previous day.
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 acclimatised 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 fluctuation in temperature over day and night times often occurs in growing facilities where 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 a low-control environment the ﬂuctuation between the target values should possibly be kept low, between 2%-4%.
However, here 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 w
eather the difference in temperature will not be that significant. In such cases the higher value needs to be approximated.
Day / Night Fluctuations
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 a computer control system such as Trutina can assist this situation.
Growers can set the value of the day / night difference as a percentage, and at which point to start the irrigation.
When the water content of the growing medium reaches or exceeds this value the computer sends an alarm message, providing the ideal timing for the start of our first irrigation.
Now that time is set for the first irrigation of the day, the next question is about aligning the moisture content to be the same as the maximum yesterday.
An increased dose of water is usually chosen in order to reach the daily maximum water content quickly.
Thirdly, the irrigation strategy should aim for only a 1 – 3 % fluctuation in the moisture content of the growing medium between waterings.
This is where you measure and consider your drain water and run off.
Optimal values may differ in both directions depending on your geographical and climatic conditions, and the current state of the plant.
Care needs to be taken in the dosage rate as well as the times in between irrigation, as both play a role in overall moisture content.
A computer alarm can be set to signal the values outside the given range, so you can appropriately respond to changes in circumstances.