How to avoid calcium deficiency in food crops in a controlled environment – Advice Eating

Leaf scorch and blossom end rot are symptoms of calcium (Ca) deficiency. Sometimes, when a nutrient deficiency occurs, the first thought is to add the nutrient that appears necessary to solve the problem. This is not always the best way to solve the problem.

Calcium plays a very important role in the formation of plant cell walls. If calcium cannot reach new cells in time, cell wall formation cannot be completed. As a result of cell death, necrotic (dead) tissue can develop in the leaves (leaf smut) and fruits (blossom end rot). Because of this, calcium uptake from the roots to the leaves is a very important process.

Calcium Movement in Plants
The main force that moves calcium through plants is water. When plants perspire, calcium moves. Calcium is only present in plants when water is moving. Most cases of calcium deficiency in greenhouse crops are due to environmental conditions, not a nutrient deficiency directly related to the nutrient solution applied.

Calcium deficiency triggers
There are several environmental conditions that can trigger calcium deficiency. The most common factors include:

Low relative humidity. When plants are exposed to low relative humidity, small pores in the leaves called stomata close. Stomata are responsible for perspiration. Calcium movement is entirely dependent on the behavior of the stomata. It is important to know the optimal relative humidity for each crop and to keep the humidity as even and constant as possible. Humidity in a greenhouse can be increased by running water through evaporative cooling mats and/or installing a misting system if needed.

Lack of airflow over crop. There must be air movement around the leaves to ensure continuous gas exchange. The friction between the leaf surface and the moving air can reduce the airflow speed around the plant leaves. This creates a boundary layer, which is a layer of heavy air that can reduce gas exchange in plants. This reduction in gas exchange can affect calcium uptake by plants.

This reduction in calcium absorption is common in greenhouse lettuce. Lettuce has a very dense canopy. New leaves are usually exposed to a very dense boundary layer. Good airflow over the canopy is necessary to avoid tip burns. Installing vertical fans is usually recommended to improve airflow in lettuce greenhouses. It is also important to maintain adequate airflow in vertical farms. For leafy greens, an air speed of 1 meter per second in each vertical layer is recommended.

High light intensity in vertical farms. When it comes to indoor farm production, there are many variables that need to be controlled to ensure good harvest performance. Two variables that together can trigger tipburn are light intensity and boundary layer. When plants are close to the grow lights, the light intensity tends to increase and the space for airflow to decrease.

When plants are exposed to the same photoperiod throughout the production cycle, the total daylight integral (DLI) tends to increase over time. Recent research has shown that in vertical indoor farms, plants exposed to a DLI greater than 17 moles of light per square meter per day (mol m-2 d-1) for more than three days induce peak burns.

High VPD values. Some crops, including tomatoes, show top burn under high VPD values. Transpiration from roots to leaves increases in a high VPD environment. When the VPD for tomatoes is too high, calcium uptake goes straight from the roots to the leaves, bypassing the fruit. Therefore, blossom end rot (calcium deficiency in fruits) sometimes occurs in tomato fruits, but no deficiency symptoms appear on the leaves.

Avoid calcium deficiency
When plants are found to be calcium deficient, be sure to check that the fertigation system is working properly. If fertilizer stock solution is kept in multiple tanks, check all reservoirs to ensure they have the same solution levels so all nutrients are distributed evenly to all plants.

However, remember to always monitor environmental conditions before adding calcium to a culture. Excess calcium can cause other nutrient deficiencies. If the decision is made to apply foliar calcium, this treatment is required throughout the production cycle to avoid calcium deficiency. Calcium applications on the leaves to prevent calcium deficiency can be avoided if the production environment is properly controlled.

For more informations:
Hoard America
Chris Higgins, CEO

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