Influence of plantation-type forests on forest soil fertility indicators under conditions of the Western Forest-Steppe of Ukraine

There is a close interaction between plantations of different composition and soil fertility which can be adjusted by changing the species involved in the stand composition. The issue is particularly relevant from the point of view of the introduction of plantation forests in place of low-yield forest stands. Therefore, the study of changes in soil fertility indicators in the system: plantation stands → soil → primary forest stand is an extremely important factor in ensuring high productivity and biotic stability of forest phytocoenoses. The investigated dark-grey podzolized soils on loess loams are characterized by high forest growth potential, the result of which is the formation of pure and mixed stands of larch and spruce of high site classes – from I to Ic. At the same time, the values of soil fertility indicators (humus content and NPK mobile compounds) under these stands are different. The humus content in the soils under plantations with the participation of spruce varies from 0.32 to 4.52% and averages 1.80%, which is lower than those under larch plantations – 0.32-9.32% and 2.17 %, respectively. The composition of plantations affects the content of all the studied nutrients in the soil. The average content of lightly hydrolyzed nitrogen in soils under plantations with spruce is lower (5.68 mg / 100 g of soil) than with the participation of larch (7.10 mg / 100 g of soil) and drops down the profile more amplitude-like. Thus, its content in the horizon He is 9.63, in HI – 4.87, in I – 2.52 mg / 100 g of soil; under the stands involving larch, these values are 10.41, 6.51 and 4.24 mg / 100 g of soil, respectively. The average content of mobile phosphorus compounds in both types of the plantations was quite similar – 5.93 (with the participation of spruce) and 5.80 mg / 100 g of soil (with the participation of larch). However, in the I-horizon under pure and mixed larch cultures, it is significantly higher in the stands with the participation of spruce – 7.70 vs 2.64 mg / 100 g of soil, which contributes to increasing the site class of larch stands to Ib-Ic classes. The nature of exchangeable potassium distribution in the soil profile is fundamentally different. Thus, under the plantations with the participation of larch its highest content (9.50 mg / 100 g of soil) was recorded in the He-horizon, whereas with the participation of spruce – in the I-horizon (11.85 mg / 100 g of soil), which indicates fairly intense process of acid hydrolysis in soils under the influence of spruce litter. At the same time, its average profile content in the soils under the study cultures is similar - 8.90 in cultures with larch and 9.17 mg / 100 g of soil – with spruce. On the whole, pure spruce and larch plantations under conditions of fresh and moist fertile site types of the Western Forest-Steppe of Ukraine do not adversely affect the fertility indicators of the dark-grey podzolized soil. However, the more favorable nutritional properties of soils are formed under plantations involving larch, which, in turn, provides a high level of their productivity, which must be taken into account when designing the composition of plantation-like stands.