On average, more growers have calcium (Ca) related problems than any other nutrient. These problems occur in areas of low humidity and high temperatures. It forms part of cell walls and any deficiency is marked by the breakdown of cell tissue leading to some form of internal “browning” of the tissue. The average concentration in the plant varies between 0.2 – 1.0%. Calcium plays an important part in the following:
- Cell division and elongation
- Cell structure
- Permeability of cell membranes
- Enhances the uptake of some nitrogen forms
- Helps with the transport and retention of other nutrients within the plant
- Protein synthesis
- Carbohydrate translocation
It can be seen that if calcium is absent, the plant will stop to grow. It is important to note that the demand for calcium is continuous and any reduction in the concentration of the element in the nutrient solution will influence the plant metabolism immediately. The reason is that calcium is not very mobile in the plant. It cannot translocated calcium from area of high concentration to low concentrations quick enough without any damage. When plants are under stress, such as low water availability, imbalances in nutrient concentrations and disease pressures, the calcium movement can be restricted due to the formation of organic acids within the vascular system. The organic acids precipitate calcium rendering it useless for plant growth.
Calcium is supplied as calcium nitrate (CaNO3). The use of ammonium nitrogen will induce calcium deficiency symptoms since ammonium is antagonistic to calcium uptake. That is one of the reasons that the ammonium levels in the nutrients solution should not be more than 10-15%, as has been mentioned in previous sections. Calcium is taken up as Ca2+ and is absorbed at the root tip so any condition that restricts root growth will restrict its uptake.