Potash fertilizers are classified into low- and high percentage. These fertilizers are classified as low-percentage, which include below 25% K20. Potassium in potassium fertilizers occurs in the chloride or sulphate form. Potassium fertilizers are obtained from crude potassium salts – minerals. After processing, the following potash fertilizers are delivered to the market: kainity, concentrated potassium salt and potassium sulfate.
Kainit contains 14-18% K20 i 7-9% MgO. It is a ground mineral, containing many admixtures of accompanying salts, m.in. table salt and magnesium sulfate; some micronutrients may also be present, most often boron. Fertilizers, relatively high in magnesium, are sold under the name of Magnesium Kainite. Kainite is also used to remove weeds by spreading it over weeded soil. These fertilizers cannot be applied to fruit plants and vegetables for a long time, because they contain a large amount of chloride, to which all horticultural plants are sensitive.
Concentrated potassium salt, obtained from the processing of minerals, contains 50-60% K20 and is the most commonly used chloride fertilizer. It can be used to fertilize plants that are less sensitive to chlorides. It is particularly suitable for heavy soils and low in calcium carbonate.
Potassium sulfate, produced in fertilizer plants, contains 48-52% K20. It is white, crystalline, not very hygroscopic, convenient for sowing. It is used for plants sensitive to chlorine, such as: white and red currants, gooseberry, raspberries, grapevines and cherries, and from vegetables under. spinach, lettuce, onions, cucumbers, tomatoes and beans. Potash fertilizers are generally used before sowing, as potassium is retained by the sorption complex. After sowing, it should be mixed in a layer of at least 20 cm. Potash fertilizers can also be used for top dressing.
Magnesium fertilizers, containing only magnesium, are not produced by us. Technical magnesium sulfate, containing 16% MgO, it is used on slightly acidic soil, neutral and alkaline, most often, however, for foliar fertilization of plants. Plants are sprayed when a magnesium deficiency is evident 2% with a solution of magnesium sulfate. Such spraying is used 3-6 times after flowering, at weekly intervals.
The second magnesium fertilizer is kieserite, a mineral containing magnesium sulfate, used for the production of calimagnesia (mixed with potassium sulfate). Magnesium fertilizers also include dolomites mined in Lower Silesia, containing 20% magnesium oxide and 31% calcium oxide.
The amount of magnesium fertilizer for vegetable plants depends on the magnesium content in the soil and ranges from 1 do 4 kg of magnesium sulfate per 100 m2. The doses for fruit plants are: on 1 tree 1-2 kg, on 1 shrub 0,5-1 kg of magnesium sulfate. Similar doses are used for strawberries and raspberries, as for vegetables. On strongly acidic soils, magnesium is leached into the deeper layers; in that cases, most often on light soils, its deficiencies may occur.