This study aims to show a value of using radioactive soil redistribution tracer ¹³⁷Cs together with soil-morphological method and empirically-based modeling for quantitative comparison of conventionally cultivated arable slopes with morphologically similar slopes where various soil-protective techniques have been applied.

Three pairs of arable slopes were selected for comparison, all located within the territory of the Novosil experimental station (the Orel Region, central European Russia). The research area is characterized by grey forest soils formed on the Late Pleistocene loessy loams. Natural vegetation was represented by the forest-steppe zone communities, but at present most of the area is cultivated. The slopes studied undergone creation of artificial terraces with forest shelter belts located parallel to topography contour lines and spaced at approximately 100 m from each other. Construction of terraces and tree planting was commenced in 1932.

Considering the multi-technical approach in which soil morphology, empirical-based modeling and ¹³⁷Cs tracer were used for assessing soil redistribution rates, it is important to note the different timescales, for which the independent techniques used are applicable. The soil-morphological method yields an integral assessment of soil degradation over the entire cultivation period (100 to 250 years for different studied slopes). The ¹³⁷Cs radionuclide tracer provides the short-term of average soil redistribution by water and tillage since 1986, because the territory was subject to intensive radioactive fallout after the Chernobyl accident (more than 90% of the total isotope inventory). The empirical model utilizes a combination of the USLE-based approach for estimating rainfall-induced erosion and a model developed by the Russian State Hydrological Institute for estimating erosion from snowmelt runoff. Its temporal resolution depends on the details of meteorological data available and ranges from a single runoff event to the entire cultivation period. We have applied it for estimating average annual erosion rates for pre-Soviet period, collective farming period and post-Soviet period, which differ substantially in terms of crop rotations and cultivation techniques used.

Preliminary results have shown that slopes with soil-protective measures are characterized by up to 30% reduction of average soil redistribution rates, as shown by soil-morphological and ¹³⁷Cs methods. Good coincidence of spatial patterns of soil redistribution rates provided by these two techniques suggests general reliability of results. Discrepancy in values obtained can be attributed to differences in temporal resolution of methods as well as to possible influence of individual extreme events on results yielded by the ¹³⁷Cs method. On the other hand, more significant decrease of average soil degradation rates on slopes with soil conservation (up to 70-75%) was predicted by the model. This substantial difference between predicted and directly measured values is attributed to a high degree of soil degradation prior to introduction of protective measures (reflected by the soil-morphological method) and lack of funding for maintaining the appropriate conditions of terraces and forest shelter belts after the collapse of the former Soviet Union (reflected by the ¹³⁷Cs technique). It can be generally concluded that the multi-technical approach acquired much more detailed information on temporal and spatial variability of soil redistribution rates than for single method-based studies.

Keywords: radioactive tracer, soil redistribution rates, soil erosion, soil morphology, ¹³⁷Cs.