It is absolutely necessary to have a full chemical analysis of the minerals and trace elements in the water used.
This will allow adjustment of the acidity and enable the conductivity (content of salts) to be planned deliberately.
The water available on site should be subjected to chemical analysis before being used for anything, for water is never entirely pure: it picks up minerals from the materials it flows through or is contained in. Analysis lets us know exactly which substances are present and in what quantities.
On the basis of this analysis we can decide whether to use it for watering, and work out what nutrients need to be added to those already present. The quantities to be added will be the quantities desired less those the water already contains.
The quality of the untreated water is liable to vary over time, and analyses will have to be repeated more or less frequently depending on this variability. They must be done professionally by a laboratory competent for this work.
Variables that may be analysed include pH, EC (electrical conductivity), main elements (nitrate, phosphorus, potassium, sulphur, calcium and magnesium) and trace elements (boron, copper, iron, manganese, molybdenum, zinc). It is important to use the same laboratory for analysis throughout the year, since methods and materials of analysis may vary from lab to lab and samples will not always produce the same results at each. This is not too bad a problem since it is mainly the variations between one analysis and the last that matter.
Pure water has a pH of 7. Natural water, however, tends to be very rich in carbonates (HCO3-), usually containing calcium. In such cases the pH is more alkaline and can discourage mineral uptake by plants, blocking ions of iron and other trace elements. What is more, limescale deposits can be left on the leaves when watered with sprinklers.
There may also be chloride,nitrate and sulphate ions which will increase water hardness.
The pH may be lowered to the level chosen by adding acid. Mineral availability is better in slightly acid soil (5.6 – 5.8).
When the water used for making up the nutrient solution is rich in carbonates, it has a high buffering potential: more acid is required to lower the pH; and, inversely, this buffering action damps down violent swings in pH which can otherwise lead to ion precipitation.
Another problem can arise from the common salt content, of Na+ and Cl- ions. These two ions are not necessary to the plants, and may build up in the growing medium, though they rarely cause plant poisoning problems.
Some trace elements may also be toxic if too much is present: this applies to aluminium, manganese, copper, zinc, molybdenum and others.
The estimate is that the total content of salts in the water used should not exceed 750 mg/l.
Maximum values for the individual elements are as follows:
Chlorine................... up to 80 mg/l
Sodium.................... up to 60 mg/l
Sulphate.................. up to 150 mg/l
Nitrate...................... amounts above 50 mg/l to be taken into account when adding fertiliser
Potassium................ amounts above 30 mg/l to be taken into account when adding fertiliser
Calcium.................... up to 200 mg/l
Magnesium.............. amounts above 30 mg/l to be taken into account when adding fertiliser
Iron ...................... up to 0.5 mg/l
Manganese.............. up to 0.5 mg/l
Boron .................... 0.5 to 1 mg/l
Zinc ...................... up to 0.5 mg/l
Finally, water may contain residues from plant protection products such as weedkillers. This applies mainly to surface water; and is a comparatively minor phenomenon.
This advice sheet is based on the methods used at the SCEA at Montourey (Fréjus, France). These procedures may need some modification to adapt them to other climatic situations. Before starting to grow cyclamen there needs to be a review of precautions against pests and diseases. We must point out that our advice and suggestions are offered for information purposes and therefore cannot include any guarantee of specific results; it is a good idea to carry out trials beforehand.
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83600 Fréjus - France
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