The element chlorine is ubiquitous in nature, and occurs in aqueous solutions as the anion chloride (CI-). In this form it is also readily taken up by plants and average chlorine contents in plant tissues are in the range of 2-20 mg g-1 dry matter. In most plant species the requirement for optimal plant growth, however, is 10 to 100 times lower which means that chlorine is a typical micronutrient. Because it is usually supplied to plants as chloride from various sources (soil reserves, irrigation water, rain, fertilisers, air pollution), chlorine deficiency is rarely found. On the contrary, there is much more concern about chlorine toxicity world-wide. Plant species vary greatly in their susceptibility to high chloride concentrations in the soil solution and four main groups in this respect can be distinguished:
The grouping of crops according to the classification as well as the recommended potassium fertilisers are shown in the following Table.
| Classification | Crop | Product |
|---|---|---|
| Chloride - loving: Chloride based fertilisers are preferred. |
Sugar beet, fodder beet, celery, Swiss chard,coconut | Muriate of Potash (MOP) Korn-Kali Magnesia - Kainit |
| Chloride tolerant: Chloride based fertilisers can be used but most vegetables prefer sulphate based fertilisers because of their sulphur demand. |
Cereals, maize, oilseed rape, asparagus, cabbage, beetroot, rhubarb Grassland, clover, oil palm, rubber, rice, groundnut, cassava, soybean, sugar cane, banana, cotton | Muriate of Potash (MOP) Korn-Kali Magnesia - Kainit |
| Partly chloride tolerant: Chloride based fertilisers can be used if they are applied on time before the start of vegetative growth. |
Sunflowers, grape vines, stone fruits, blackcurrants, seed potatoes, potatoes for human consumption, tomatoes, radish, kohlrabi, peas, spinach, carrots, leek, horse-radish, chicory, pineapple, cucumber, kiwifruit, coffee, tea | Sulphate of Potash (SOP) Patentkali Korn-Kali |
| Chloride sensitive: (Only fertilisers containing potassium in the form of sulphate should be used). |
Starch potatoes, potatoes for processing, tobacco, redcurrants, gooseberry, raspberry, strawberry, blackberry, blueberry, mango, citrus, pepper, chilli, avocado, cashew, almond, peach, cocoa, hops, pomes and stone fruits (especially cherries), bush beans, broad beans, cucumber, melon, onion, lettuce, early vegetables, all crops under glass, conifers, flowers and ornaments as well as seedlings and transplants of most plants | Sulphate of Potash (SOP) Patentkali |
The effects of high CI- concentrations in the soil solution on yields of various crops is shown in the following graphs. The steeper the yield decline with increasing CI- soil concentrations the more sensitive to chloride is a crop and hence the better will be the response to virtually CI- free fertilisers, e.g. SOP and Patentkali.
Prior to these substantial yield depressions, uptake of large amounts of chloride may lead to negative effects on crop quality such as:
To avoid yield, quality and hence income losses in chloride sensitive and especially high value crops, where quality counts, the use of our low chlorine potassium fertilisers, SOP and Patentkali is recommended.
