Calcium chloride is a widely used fertiliser in chicory witloof forcing. "We often see striking improvements: the heads are of better quality, the yield is higher and, in particular, the bacterial disease pressure is lower."
Accelerating and retarding effects
Calcium (Ca) is an important element in the development of plant cells, and its functions include promoting the rigidity of the cell walls. Calcium has limited mobility in plants. However, research has revealed that chloride ions play a beneficial role in transporting and distributing calcium ions through plant tissue: conversely, nitrates retard this process. Experiments in which chicory root crowns were sprayed with a calcium chloride solution containing a radioactive isotope of Calcium, Ca45, revealed that the radioactive isotope reached the growing point (the pith). Consequently, a treatment with calcium chloride is ideal for the rectification of any calcium deficiency. Nitrate and sulphate-rich environments retard the distribution of calcium through the plant tissue. In addition, some cations (positively-charged ions) - ammonia, potassium and sodium - are antagonists: they can displace calcium ions from the tissue. Conversely, borate ions (boron) enhance calcium assimilation.
Improved quality, fewer pith anomalies
Calcium chloride's beneficial effect in chicory cultivation is based on the alleviation of a calcium deficiency in the chicory roots, thereby reducing problems with brown and glassy pith and black tip. In addition, the heads are often firmer, with a more glossy appearance. Moreover calcium chloride has an antibacterial effect, and would appear to enhance the effect of some fungicides (research has demonstrated that calcium chloride enhances the effect of Rovral in controlling Sclerotinia). In conclusion, an immersion in calcium chloride solution has an effect on the rehydration of the roots, thereby partially nullifying moisture loss during storage: it is known that a moisture loss of just a few per cent during chilled storage is sufficient to reduce yields.
Immersion has the greatest effect
The best effect is obtained when the chicory roots are immersed in a calcium chloride solution (approx 30 grams/litre). The best time for this treatment is 2 weeks before planting. After immersion, the crates must be returned to the chilled storage for at least 2 weeks. Many French growers use the shower method, whereby the calcium chloride solution (approx. 30 grams/litre) treatment of the 1 m3 crates is continued until all the roots in the crate are moist. The excess solution is recovered and re-used. A lower concentration is used on early chicory roots that have just been lifted (approx 15 g/l).
Spraying is an alternative
If immersion or a shower is not an option, it is also possible to spray the roots (the crown) with approx. 50-120 grams/l/m2. This is based on a fertiliser with approx. 80% calcium chloride. If necessary, this concentration can even be increased for early forcing using roots with a large crown of leaves. Conversely, a lower dose is required for very bare roots to prevent salt damage. Calcium chloride can be mixed with boron. Use a maximum of 0.8 g/l/m2 boron when spraying the tips: this is equivalent to 4 grams of Solubor (20.5% B). Prepare a mixture with calcium chloride by dissolving the Solubor and then adding the calcium chloride.