Physicochemical properties of soils in the forest-park stands of Kyiv city

The experimental plots were established in natural forest stands of mature and overmature ages in different edatopes of forest growth – A2, B2, B3, C2, C3, D2 (according to Alekseev-Pogrebnyak's edaphic net). Forest stands formed mainly by Pinus sylvestris L. and / or Quercus robur L. The investigated natural forest stands are characterized by high forest plant effect, which can be explained by the favorable values of the soil’s physicochemical properties (pHH2O, pHKCl, amount of absorbed bases, absorption capacity, degree of saturation of bases).The analysis of physicochemical properties of soils in the forest-park stands of the Kyіv city makes it possible to formulate conclusions. First, the numerical value of the soil-absorbing complex of sod-podzolic soils of clay-sand mechanical composition is negligible. The saturation of the soil-absorption complex by the cations of alkaline earth metals and hydrogen is evidenced by the data of the absorption capacity, which range from 4.7 to 10.7 ‒ in the humus-eluvial horizon, as well as from 2.0 to 5.8 mg ‒ еq. per 100 g of soil ‒ in eluvial horizon. The fact of decrease of this index from the upper layers to the lower ones has been established, and a considerable increase is observed at the near occurrence of moraine sediments.Sums of absorbed bases, as well as the absorption capacity in the upper layers of all soils are close in value. The surface layers are characterized by significant amounts of the sums of the absorbed bases due to the accumulation of bases in the course of bio-circulation ‒ up to 3.3 mg ‒ eq. per 100 g of soil. In fresh submerged conditions (edatope B2), the maximum value of the sum of absorbed bases was fixed in the humus-eluvial layer of the rich difference of fresh subsidence (edatope B2///) ‒ 5,25 mg ‒ eq. per 100 g of soil; the absorption capacity in this layer reaches 10.41 mg ‒ eq. per 100 g of soil. In edatopes B2/ and B2//, the sum of absorbed bases is negligible ‒ 0.10‒2.01 mg ‒ eq. per 100 g of soil, with the absorption capacity of 2.33‒9.07 mg ‒ eq. per 100 g of soil. Within these limits, the values of these indicators fluctuate in edatopes A2, B3, C2, C3. But in the deep layers of the soil profile (in places of occurrence of the mother soil), the value of this indicator increases again: in pine sand — up to 3.61 mg ‒ eq. per 100 g of soil, moraine sandy loam or loam of fresh suburbs ‒ up to 3.7, moraine light loam in edatope C2 ‒ up to 4.94 and in boulder clay ‒ up to 15.5 mg ‒ eq. per 100 g of soil. In the case of oak forest, that grow on fertile soil in fresh moisture conditions (edatope D2), the sum of absorbed bases and absorption capacity have the greatest values at depths of 20‒40 cm (8.88 mg – eq. per 100 g soil and 17.9 mg – eq. 100 g soil respectively). The smallest values of these parameters were set at a depth of 62‒100 cm (respectively 4.25 mg ‒ eq. per 100 g soil and 6.7 mg – eq. per 100 g soil). Among the studied edatopes, the highest sums of the absorbed bases are characterized by the soil thickness of edatopes C2 and C3, where this index reaches 82 %. The actual acidity (рНН2О) values indicate that the upper layers of sod-podzolic soils under fresh boron conditions (edatope A2) are characterized by a weak acid reaction (5.0‒5.5). The magnitude of this indicator deviates toward the midacid reaction in edatopes B2// and B2///, approaches neutral reaction (5.5‒6.0) on relatively rich soils in fresh and moist conditions of moisture (edatopes C2, C3) ‒ in proportion to the increase in Q. robur participation in forest stands. Such actual acidity (рНН2О) contributes to the development of mycorrhizal fungi, the normal nutrition of P. sylvestris and its successful growth. With the depth of the soil thickness, there is a general tendency to neutralize its acidity. The value of the exchange acidity (pHKCl) of the surface layer of soil under pine stands is within the strongly acidic (4.0‒4.5), and in pine-oak forests this indicator varies between strongly acidic and slightly acidic (4.6‒5.2). In the surface layer of soil of pine forest stands, рНKCl is strongly acidic (4.0‒4.5), and under pine-oak forests it varies between strongly acidic and slightly acidic. On the example of oak and pine-oak stands that are growing on fresh and moist relatively rich soils (edatopes C2 and C3) the peculiarity of distribution of actual acidity in the surface layer of soils beneath them is revealed. This feature is that the weakly acidic рНН2О reaction approaches to neutral with increasing proportion of Q. robur in the stand’s composition:1/10 of the total forest stand stock is Q. robur and 9/10 is P. sylvestris ‒ pHH2O is 5.0; 3/10 parts is Q. robur and 7/10 parts is P. sylvestris ‒ 5.5; 8/10 parts is Q. robur and 2/10 parts is P. sylvestris ‒ 5.7; 10/10 parts is Q. robur ‒ 5.9.