Litter removal, paving, trampling, even turfing of the surface under the trees impedes or prevents the circulation of nutrients between the soil and the plant, Moreover, they worsen air and humidity relations.
The size of the nutrient loss to trees can best be assessed, when the nutritional needs of individual species are compared with the amounts of components returning to the soil in the form of fallen leaves forming the litter. In forest conditions, lime stands return over the mulch 50% nutrients taken. The birch stand returns much less components. The older the tree, the higher the mineral content of the leaves, and thus more of these components are returned to the soil. As a result of removing the litter, the nutrient deficit in the soil increases.
Table. Nutrients taken up and returned to the soil during the year by different stands depending on their age.
Losses caused by raking litter mainly concern nitrogen, potassium and calcium, which is confirmed by chemical analyzes of the leaves; the results of these analyzes are presented in the table and the table below.
Table. The content of the most important nutrients (except for nitrogen) in the leaves of some tree species approx 35 years.
Percentage of nitrogen content in the leaves of some tree species:
Robinia pseudoacacia 3,4
Alnus incana 2,8
Tilia cordata 2,3
Acer pseudoplatanus 2,3
Acer saccharum 1,7—2,8
Corylus avellana 2,1—2,3
Quercus sp. 2,3
Quercus borealis 1,8—2,4
Fagus sihatica 1,7—2,2
Tilia platyphyllos 2,2
Fraxinus excelsior 1,7—2,1
Salix caprea 1,9
Ulmus sp. 1,8
Sorbus aucuparia 1,8
Betula verrucosa 1,7
Alnus glutinosa 1,4
Carpinus betulus 1,2
Pinus silvestris 1,3—1,8
Larix sp. 1,1—1,9
Picea excelsa 1,1—1,8
So far, no data are available on the leaf mass produced by urban trees. Data on the physiology of forest trees are not completely reliable in urban conditions. Raking the litter in forests, however, has always caused disadvantages, and sometimes even catastrophic habitat degradation. It is worth mentioning here, that free-standing trees produce more mulch than compact growing trees, so in cities, where the former predominate, the losses due to raking fallen leaves are even greater.
The deficiency of individual nutrients in the plant can be determined on the basis of external symptoms. In the case of nitrogen deficiency, the leaves show a light green discoloration, becoming yellowish as the deficiency increases. Leaves
and shoots become smaller and thinner. Deficiency symptoms
they usually occur all over the tree. Potassium deficiency reduces shoot growth, until it stops completely. The leaves are small and often have a bluish-green tinge. A symptom of potassium deficiency may be the dieback of the edges of the leaf blade.
Losses caused by leaf removal can be at least partially compensated by adequate fertilization. However, the lack of established formulas for fertilizing trees in urban conditions makes this activity difficult. The demand of individual tree species for basic nutrients - N:P:K kształtuje się jak 1 :1 : 0,6. In Germany, a fertilizer mixture is used under the name "Baumfutter", which contains significant amounts of organic nitrogen. The ratio of N: P: K is in it 1:1:2, and the percentage of pure ingredients - 7:7:13.
In the USA, fertilizer mixtures are used, in which the ratio of N:P:K is 1,0: 0,8: 0,6. These mixtures are mostly nitrogen in the form of organic compounds. The amount of fertilizer needed is practically determined by the thickness of the trunk of the fertilized tree. On 1 cm diameter of the trunk should fall, depending on the size of the crown, N 14—28 g, P 14—28 g i K 26-52 g.
When fertilizing trees growing in groups, 4-8 kg of the N-ratio mixture is used:P:K = 10:6:4 on 100 m² terenu.
The doses of fertilizers should depend on the purpose of fertilization. If, for example, the tree is young and we want to get a quick increase in its mass, it will be justified to increase the doses of fertilizers. In urban conditions, it is recommended to fertilize the following trees:
1) growing on lawns;
2) growing on soils covered with impermeable surfaces;
3) growing on poor soils;
4) undergoing surgery; fertilization necessary from the year preceding the treatment up to several years after the treatment.
The aim of fertilizing trees should be to supplement nutrient losses. It is better to use slow-acting fertilizers to fertilize older trees, thanks to which it is enough to use this treatment every few years.