When a nutrient deficiency occurs in plant development, the first thing that comes to mind to solve the problem is to add the necessary nutrient. This solution may not always be the right way.
Calcium has a very important role in plant cell wall formation. If calcium cannot reach new cells in a sufficient time, cell wall formation cannot be completed. This can cause necrotic (dead) tissue in leaves (tip blight) and fruit (blossom end rot) as a result of cell death. Therefore, calcium uptake from the roots to the leaves is a very important process.
Movement of Calcium in Plants
The main force that moves calcium in the plant is water. Calcium moves when plants sweat. Calcium is only found in plants when water is on the move. Calcium deficiency in plants grown in a greenhouse environment is usually not directly related to the nutrient solution, but is caused by environmental conditions.
The most common factors that can cause calcium deficiency are:
Low Relative Humidity
When plants are exposed to low relative humidity levels, tiny pores in leaves called stomata, which are responsible for transpiration, close. Calcium movement in plants is completely dependent on stomatal behavior. It is important to know the optimum relative humidity levels for each crop and to keep humidity levels as uniform and consistent as possible. Humidity in a greenhouse can be increased by running water through cooling pads and/or installing a mist system if necessary.
Lack of Airflow over the Crop
There must be air movement around the leaves to ensure continuous gas exchange. Airflow velocity around plant leaves may decrease as a result of friction between the leaf surface and moving air. This creates a boundary layer, a heavy layer of air that can reduce gas exchange in plants. This reduction in gas exchange can affect calcium uptake by plants.
This reduction in calcium intake is common in greenhouse lettuces. Lettuce has a very tight leaf layer. New leaves are often exposed to a very dense border layer. Good airflow over the crop leaf layer is required to prevent tip blight. To improve air flow in lettuce greenhouses, it is often recommended to install vertical fans. It is also important to ensure proper airflow in vertical farms. For leafy greens, an air velocity of 1 meter per second per vertical layer is recommended.
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High Light Intensity in Vertical Farms
Controlled crop production indoors has many variables that need to be controlled to ensure good crop performance. One of the variables that can cause tip burn is the light intensity and the other is the boundary layer. The increased light intensity due to placing the plants close to the grow lights results in a reduction in the airflow area.
If plants are exposed to the same photoperiod throughout the entire production cycle, the total daily light integral (DLI) tends to increase over time. Recent research has shown that tip blight is triggered in indoor vertical farms when plants are exposed to a DLI exceeding 17 moles of light per square meter (mol·m-2·d-1) per day for more than three days.
High VPD (Air Temperature and Vapor Pressure Gap) Levels
Some crops, including tomatoes, show tip blight under high VPD levels. In a high VPD environment, transpiration from roots to leaves increases. When the VPD is too high for the tomato, the calcium intake goes directly from the roots to the leaves, bypassing the fruit. For this reason, blossom end rot (calcium deficiency in the fruit) sometimes occurs in tomato fruit, but deficiency symptoms are not seen on the leaves.
Preventing Calcium Deficiency
If the plants are deficient in calcium, check that the fertilizing system is working properly.
If fertilizer stock solution is maintained in more than one tank, check all reservoirs to ensure the same solution levels so nutrients are distributed evenly across all crops.
But always remember to monitor environmental conditions before adding calcium to any crop. Excess calcium can cause other nutrient deficiencies. If it is decided to apply foliar calcium, this application is necessary throughout the entire production cycle to prevent calcium deficiency. Foliar applications of calcium can be avoided to prevent calcium deficiency if the production environment is properly controlled.