OVER-COMPACTION CHERNOZEMS OF THE PRYDNISTERSKA UPLAND UNDER CONDITIONS OF AGROTECHNICAL IMPACT

Abstract

The article presents the results of the study of an agrotechnical influence on the general physical properties of arable chernozems of the Prydnisterska upland. The obtained results are aimed not only at the elucidation of the problem of over-compaction but also at the determination of the features of the agrogenic transformation of physical properties on the plains and slopes of arable chernozems of the study area. The data from analytical studies and the use of GIS technologies allowed to characterize the heterogeneity of the resistance of arable chernozems to the agrotechnical impact impact, to localize abnormally compacted slope areas and to visualize spatial differences in the manifestation of over-compaction of arable chernozems.
 In today's conditions, the mechanical cultivation of chernozems, as a factor in regulating agrophysical properties, is an integral part of technological operations in the agricultural system. However, the irrational intensification of agriculture has led to a deterioration of agrophysical properties, which directly affected crop yields, the efficiency of assimilation of mineral and organic fertilizers, and the growth of additional flow costs. The main problems that decelerate the restoration of the ecological resistance of arable chernozems to an external mechanical impact are a non-compliance with the norms of the agronomic load and a misconception about the homogeneity of the physical properties of arable land on the plains and slopes of the terrain. In particular, the results obtained in the process of the study of the physical properties of arable chernozems of the plains and slopes of the Prydnisterska upland indicate clear spatial differences that are manifested in the horizontal and vertical directions. Compared with the plains, the density of arable chernozems on the slopes increases with the increasing steepness of the terrain. Thus, in the upper parts of the gentle slopes, the density of the structure (in the layer of 0 – 20 cm) within the slopes with a steepness of ≥ 7 ° increases by 12-16%. To some extent, this can be explained by the decrease in the capacity of the humus-accumulative horizon and the involvement in plowing of the lower transitional soil horizons with the relatively low porosity.
 The analysis of the profile distribution of structural density indicators showed a certain variability of compaction, which is manifested with depth. Naturally, the smallest values of the density of the structure are recorded within the arable horizon, which is constantly exposed to agronomic influence. However, starting from the depth of 20 cm there is a sharp compaction of the soil layer. For example, in the plain watersheds the over-compacted stratum with the index ≥1.4 g / cm3 reaches the depth of 40-50 cm, and within the slopes it reaches the mark of 60 – 65 cm. The density of the chernozem structure beneath a subsoil horizon significantly decreases, especially in the presence of carbonates and areas with an active zooturbation (areas with moles, numerous ant passages and wormholes).
 The increase in the spatial heterogeneity of the physical properties of arable chernozems may be caused by the formation of abnormally compacted linear areas due to the passages of machine-tractor units. In particular, within a track formed after a single pass of a combine, the density of the structure increases by 4 – 5%, and in areas of the repeated passage of the agricultural machinery it grows to 9 – 13%.
 Based on the standards adopted in Ukraine, the chernozems of the experimental plots have undergone varying degrees of degradation due to the compaction that is identified by indicators of the porosity. Within the gentle sloping and sloping areas (soil profiles Rd–3 –4 and Sv–3 –4) a significant deterioration of the physical properties of arable chernozems of the study area is recorded. In particular, the porosity of arable and subsoil horizons indicates a predominant degree of a severe degradation. The average degree of degradation is fixed on the flat parts of the relief of the research areas, which have a significant potential in the restoration of the ecological stability of agricultural soils under a moderate agronomic load. 
 Key words: over-compaction, chernozem, plains and slopes of areas, Prydnisterska upland.