Potassium fertilizers to reduce 137Cs accumulation and increase fodder crop harvesting on the radionuclide-polluted floodplain pastures

Protective measures on the radionuclide-polluted rural territories after the Chernobyl accident are known to reduce agricultural production which is not corresponding to standards for radiation safety and a common radiation dose. On natural floodplain pastures in the southwest of the Bryansk region, we studied fodder crop yield and specific radioactivity as influenced by mineral fertilizers with regard to their total doses and potassium to nitrogen portion. The soil of the pastures was alluvial sod-gley sandy with 3.08-3.33 % humus, 620-840 mg/kg P2O5, 133-180 mg/kg K2O, and pHKCl 5.2-5.6. After the Chernobyl disaster, the post-accidental 137Cs pollution of the soils was 1221-1554 kBq/m2 in 2000-2008 and 559-867 kBq/m2 in 2009-2014. A mix of Brоmus inеrmis (8 kg/hectare), Festuca pratensis (8 kg/hectare), Phleum pratens e (5 kg/hectare), Phalaris arundinacea (5 kg/hectare), Alopecurus pratensis (5 kg/hectare) was used for sowing in 2000-2008, and in 2009-2014 Festuca pratensis (6 kg/hectare), Alopecurus pratensis (5 kg/hectare) and Phalaris arundinacea (7 kg/hectare) mix was examined. Ammonium nitrate, simple granular superphosphate and potassium chloride were as fertilizers. According to the protocol, 1/2 doses of N and K along with full P dose were pre-applied to soil at the first mowing, and 1/2 doses of N and K were applied after mowing. Minimum aboveground green biomass possessing the greatest specific radioactivity was observed when no mineral fertilizers used. In 2000 tо 2008 the highest crop yield of 30.9 t/hectare was harvested when N60P90K60 applied. An increase in N, P, K and their fractions did not lead to a significant rise in green mass production. However, at N60P90K60 dose and nitrogen to potassium ratio as 1:1 the nitrogen increased a specific radioactivity of forage which did not correspond to radiation safety standard. Therefore in the areas polluted at 1221-1554 kBq/m2 we recommend applying NPK fertilizers with N to K ratio of 1:1.5 to grow green biomass which possesses the specific radioactivity not exceeding the admissible level. In 2009 to 2014 N45P60K75 were optimal for high productivity and admissible quality of the fodder crops. With no fertilizer used the correlation between yield and specific radioactivity level was weak and positive, whereas application of fertilizers at N:K portion as 1:1, changed the correlation to weak, but negative. Further increase in K fraction strengthened the correlation. Our findings of decrease in 137Cs specific radioactivity level in green fodder confirm that the K fertilizers are mainly effective for a rehabilitation of soil radioactive pollution on pastures. 137Cs migration from forages to animal husbandry production was also calculated. So, it is shown that the K fertilizers are the main factor limiting 137Cs transition from soil to plants and thus lowering 137Cs specific radioactivity in animal husbandry products and a corresponding internal exposure dose in human.