Indication of erosive-accumulative processes intensity at using 137CS profile distribution on selected soil transect

The loss of the most fertile soil layers is induced by erosion from erosive parts of a transect. Production ability of soils goes often down in this way. In effort to assess its negative influence on the soil, it is very important to know the intensity of this process. It can be said that the negative influence of erosion is significant in case the intensity of soil loss is higher opposite its creation through the soil forming process. The paper is focused on assessment of water erosion intensity (on example of the monitored locality), using two methods and their comparison. The first one is the indication of erosive-accumulative processes intensity using 137Cs activity determination in soil profiles (profile distribution). On the basis of this method, we can evaluate the amount of eroded (or accumulated) material directly (using proportional model) or indirectly (using of caesium profile distribution). The 2nd method is the average annual soil loss calculation using empirical model of the Universal soil loss equation (USLE) under the actual soil-climatic conditions. The monitored locality (arable land) was situated in the erosive sensitive area (from the viewpoint of rainfall intensity, soil erodibility, gradient of slope, and land use), north-east from Detva town. The primary requirement for selecting the study locality was relief of surrounding area (erosive catena was located on the basis of terrain survey). Erosive catena is characterized by a typical line of pedological sites localized along the transect line (in direction of water erosion impact). The first one is on the top plateau of the slope (represents the soil uninfluenced by water erosion - referential soil profile), the second is in the erosive part of the slope (represents the soil strongly influenced by water erosion - eroded soil profile), and the last one is situated in the accumulative part of the slope (represents accumulated soil - accumulated soil profile). We have achieved the extreme value of potential soil erosion (139.6 ton per hectare and year) by numerical calculation using the USLE. It can be said that potential soil erosion expresses an inherent susceptibility of bare soils to erosion (in case the soils are protective vegetation cover free). Actual soil erosion refers to the present endangerment, taking into account a contemporary vegetation cover (silage maize in this case). The mean annual soil loss, determined by this method, was 68.4 ton per hectare and year. This value is still too high, because maize belongs to the plants with not very good anti-erosive effect. Profile distribution of l37Cs in individual parts of erosive transect indicates the presence of intensive erosive-accumulative processes. The difference in the maximum depth of still measurable radioisotope concentration in the accumulative and referential soil profiles (100 mm) indicates the depth of accumulated layer in the base of the slope for approximately 40 year period (recent erosion). The mean annual soil loss has been calculated on the basis of a mass balance. This value is about 32.5 ton per hectare and year, which is a lower value in comparison with the USLE. The calculated value expresses the average soil loss during 40 year period, when annual intensity of erosion was either very high or very low (in dependence on rainfall intensity and actual vegetation cover). Using calibration proportion model for the quantitative assessment of soil matter loss or accumulation is in this example limited by too high activity of caesium in the topsoil of referential part of the transect (in comparison with the other parts of erosive catena). Soil loss from erosive part (24.11 ton per hectare and year) was approximately similar to the soil loss achieved by using a mass balance, but the value of accumulated soil mass (from accumulative part of transect) is much lower (4.72 ton per hectare and year), what is not in correspondence with the results achieved in the eroded point. Finally, it may be said that the proportional model is based on area expression of caesium activity (Bq per square m). Therefore the calculated value from accumulative part of the monitored locality was not very precise (in spite of caesium activity measured in deeper layers of soil profile). It is due to a quite high value of l37Cs activity in the topsoil of referential part.