Macro- and micro-morphological differentiation of humus-accumulative horizon of forest soils

Abstract

The paper presents the results of studies of macro- and micromorphological differentiation of the surface humus-accumulative horizon (A) of forest soils of the steppe zone of Ukraine. The study groups included typical soil profiles of natural ravine, wall (slope of the river bank) and floodplain forests, and chernozem under grassy and artificial tree vegetation within Prisamarya Dniprovsky (Novomoskovsk district, Dnipropetrovsk region). In the macromorphological study, the method of field description of soils recommended by FAO (2012) was used, the characteristics of microstructural soil organization were described in G. Stoops (2003). The differentiation of the surface humus-accumulation horizon (A) of the investigated soils is diagnosed after changes in a number of macro- and micromorphological characteristics of the structural state-morphology and aggregate size, total porosity, void morphology, and addition density. The analysis of morphological characteristics reveals both communities the features of differentiation of the humus-accumulative horizon, and certain differences between the soils of natural forests and Calcic Chernozem. The surface humus-accumulative horizon of Calcic Chernozem, both under grassy and under artificial tree vegetation, is differentiated into two sub-horizons A1 and A2. In the Voronic Luvic Chernozem of natural ravine, Luvic Phaeozem of the pristine (slope of the river bank) forests and Mollic Fluvisol of floodplain forests, the surface horizon is differentiated into three sub-horizons – A1, A2, A3. At the macromorphological level, of the surface humus-accumulative horizon there are synchronous changes in the main characteristics of the structural state - the set and the dominant types of structure, the prevailing dimensions of aggregates within the framework of one type of structure, the total porosity, the diversity of the morphology of the voids, the relative participation of individual types of voids in the formation of pore space, density shape. At the micromorphological level, differentiation is diagnosed on the basis of changes: a set and the relative ratio of different types of microstructure; the ratio of the dominant types of voids and the total area of apparent porosity; morphology of aggregates (shape, size, degree of accomodation of surfaces, intra-aggregate porosity) within a single type of microstructure. The more complex differentiation of the surface humus-accumulative horizon of forest soils in comparison with Calcic Chernozem is due to the greater thickness of the horizon, which causes a significant compaction in the lower direction within the surface horizon and more intensive biological activity (especially soil meso- and microfauna).