Fertilizers are used to regularly collect high yields of good quality. The lack of this or that element in the nutrition of a plant has its own symptoms and appears in external changes. At the same the type of soil itself initially involve element deficiency and leads to plant nutritional disorder, which leads to leaves yellowing and falling off, shoot dieback etc. Some may mistake these symptoms for a sign of a plant disease, but, in fact, they do not need to be treated, but only to be fed with fertilizers.
Nitrogen fertilizers — inorganic and organic nitrogen-containing substances that are applied to the soil for increased crop yields. Mineral nitrogen fertilizers include amide, ammonia and nitrate fertilizers. Nitrogen fertilizers are mainly produced from synthetic ammonia. Due to the high mobility of nitrogen compounds the lack of it in the soil often limits the development of the crop plants, so the nitrogen fertilizers application causing a great positive effect. Symptoms of plant nitrogen deficiency are dwarfed growth, short and thin shoots and stems, small florets, weak plant foliage, weak branching, small narrow leaves with pale green color.
Phosphorus fertilizers — minerals, calcium and ammonium salts of phosphoric acid. These fertilizers include superphosphate, double superphosphate, ammophos, diammophos, orthophosphate, potassium metaphosphate, fertiphosphate, basic slag, phosphorite meal, bone meal, etc. Phosphorus starvation appears to change the color of leaves on purple, bronze and delay flowering and ripening. Phosphorus plays an important role in the life of fruit and berry crops. It is a component of complex proteins which are involved in the nucleus cell division and the formation of new plant organs, fruit and berry ripening, promotes the starch, sugar, and fat accumulation. Phosphorus significantly improves drought and frost resistance of plants. It plays an important role in speeding up the ripening of fruits. 
Potassium fertilizer in addition to increasing crop yields improve the quality characteristics of farmed products: increase plant's disease resistance, increase fruit keeping capacity and durability during transport, as well as to improve their taste and aesthetic qualities. Potassium fertilizers are usually used in combination with nitrogen and phosphate fertilizers.
Potassium chloride (КCl) - is a concentrated potassium fertilizer. It is a white crystalline substance and is easily dissolves in water. Potassium chloride is extremely important for its functionality mineral potassium fertilizer, potassium - the participant of the basic plant growth processes. Potassium intake in plants mineral nutrition is significantly higher than of other elements, especially for crops forming a large amount of sugar, starch, and fat. They have up to 8% of potassium.
Potassium fertilizers reduce the nitrates and radionuclides percentage income, contribute to a better absorption of nitrogen, the formation of the protein, etc. It should also be noted that the use of potassium fertilizer is a powerful factor for the root system growth, especially for fruit trees and berry bushes.
The following calculator calculates the additional required quantity of potassium chloride with the introduction of other types of fertilizers.
 Капуцкий Ф.Н., Тикавый В.Ф. Пособие по химии для поступающих в вузы.—Минск: Вышейшая школа, 1979.—С.218