In natural and undegraded habitats, trees and shrubs use the nutrients circulating in a closed circuit. Fallen leaves or other parts of plants die and, after decomposition and mineralization, are whitened again by the roots in the form of mineral salts. The food circulation of woody green areas is interrupted and approx 50% the ingredients being downloaded are not involved in it. This amount is removed by raking up the leaves and other parts of the plants each year. The worst conditions in this respect are on the streets, where the soil is fenced off with impermeable surfaces, mostly preventing the supply of fertilizers and water. Removal of leaves creates a nitrogen deficiency and, to a lesser extent, potassium.
The deficiency of some components can be determined by external symptoms. Nitrogen deficiency makes you dim green, or a yellowish discoloration of the leaves. The leaves are tiny, do not reach normal size. Shoot growth is slight. Shoots are short and slender.
Potassium deficiency causes weaker shoot growth, until it stops completely. Leaves do not reach normal size, they turn blue-green. Necrosis may occur at the edges of the leaf blades, that is, tissue dieback. The leaves curl and dry.
Poor growth, unusual coloring and leaf fall may also be caused by other factors such as prolonged drought, soil salinity, diseases and pests as well as air pollution. Making a decision about the need for fertilization must be preceded by a wider diagnosis. Therefore, the best test of soil abundance in digestible nutrients is the analysis of properly harvested soil. Tree roots, especially the elderly, they develop at considerable distances from the trunk, usually beyond the projection line of the crown edges and at depths 0,5-1,0 m. Samples should be taken at these locations. Help in determining the method of fertilization, in addition to the findings on the basis of analyzes, may be the results of visual inspection of leaves and shoots, and knowledge of the size of the losses of the various components, incurred by raking leaves (chemical analysis of leaves).
Establishing general recommendations for the amount and proportion of different nutrients in a fertilizer is complex. It depends on many factors, how: species, the age and general health of the tree, type and natural abundance of soil, type of soil cover, the amount of rainfall, soil salinity, etc..