ИСТИНА

Plowing is certainly the most significant factor for Cs-137 penetration deep into the arable soils profile. It is expected that after an accident of radioactive fallout Cs-137 distribution within ploughed horizon becomes rather homogeneous upon 2-3 years of agricultural practice as a result of agroturbations when plowing, disking, harrowing, ets. To test the assumption of Cs-137 homogeneous distribution within ploughed horizon of arable soils the study in the area with chernozem soil cover that ~30 years earlier was affected by Chernobyl fallout (Plavsky hotspot, Tula region of Russia) have been conducted. The 30-cm top layer involving current ploughed (Ap, 0-13 cm) and old ploughed (Aop, 13-29 cm) horizons have been examined separately and on a number of depths: 0-10 cm, 10-20 cm, 20-30 cm, as well as thin 3(5) cm layers. Cs-137 activities in Ap were 454±52 Bq/kg (81 kBq/m2), in Aop 420±37 Bq/kg (86 kBq/m2), and they add up to >98% of total Cs-137 in soil. This clearly demonstrated the use of deep plowing after Chernobyl accident as a countermeasure against radioactive pollution. At the same time more detailed study of Cs-137 distribution within Ap horizon have revealed incomplete homogeneity of the radionuclide in soil mass. The difference between separate layers of Ap reached 50-80 Bq/kg when analytical error for Cs-137 activity in soil not exceeded 10% (40 Bq/kg). As a rule maximal activity of Cs-137 was fixed at the depth 10-20 cm (especially in the layer 12-15 cm), which is usually excluded out of agroturbations when cereals are cultivated. So to some extent the radionuclide root uptake by cereals occurs from relatively less contaminated soil layer. The probable reason of a small decreasing in Cs-137 activities and supplies in 0-10 cm layer could be accelerated erosion in constantly ploughed topsoil accompanying with losses of thin Cs-containing soil particles. Distribution of Cs-137 within Aop horizon or within 20-30 cm soil layer also demonstrated definite heterogeneity. In this case Cs-137 activities regularly reduced with a profile depth in ≈20-25% each 5 cm, that reflecting, on the one hand, periodical input of the radionuclide from Ap during deep plowing under potatoes, and on the other – transition to subarable horizon of chernozem. Therefore, some heterogeneity of Cs-137 distribution within ploughed horizon of arable chernozems of Plavsky radioactive hotspot may be noticed even nowadays, 30 years after Chernobyl accident. Preliminary profile distribution of Cs-137 by genetic horizons and then more detailed Cs-137 quantification in ploughed (+ old ploughed) horizon(s) taking into account agrotechnical characteristics of various crops cultivation should be done for the purpose of representative radioecological assessment in this connection. The study was conducted with the support from the Russian Foundation for Basic Research (project no. 14-05-00903 and 14-05-92105).