Agrochemical aspects of the rehabilitation of radioactively contaminated flood meadows of the Bryansk region

Natural fodder lands are a fodder base for livestock production in Bryansk region. The lands cover the area of 5500 km2, its greater part was contaminated with long-lived artificial radionuclides due to the Chernobyl accident. Therefore, there was a risk of contamination of the forage for dairy livestock with Cs-137 and its content in the grass would exceed the acceptable limit. Long after the Chernobyl accident the measures to remediate contaminated floodplains in Iput River in Novozybkovsky district of the Bryansk region for further use in feed production were examined. It was found that if Cs-137 contamination density exceeded 555 kBq/m2 the radionuclide content in the mass of air-dry wild grasses would be ≥5.5 times higher than the acceptable limit depending on a harvesting period. Due to the use of agrotechnical and organizational measures to improve the quality of radiation contaminated flood meadows the Cs-137 specific activity in air-dry cultivated grasses reduced by 10% as compared with the radionuclide activity in natural/wild grasses. The use of agrochemical measures for remediation of radiation contaminated flood meadows allowed to obtain air-dry masses of wild and cultivated grasses with the acceptable limit of Cs-137 radioactivity in fodders. The maximum effect was obtained when applying mineral fertilizers with a ratio of nitrogen to potassium as 1:2. Due to the use of correlation analysis it became made evident that the presence of nitrogen fertilizer increased Cs-137 specific activity in the fodder and there was the correlation between calendar years of the study and the amount of nitrogen fertilizers in soil. The correlation between the amount of nitrogen fertilizer in the soil and the specific activity of Cs-137 in the air-dry mass of natural and cultivated grasses during the years of 2003-2008 was strong and ranged from 0.76 to 0.85. In the study periods from 2009 to 2014, the impact of nitrogen fertilizer on the radionuclide specific activity in feed decreased regardless of the harvest period of natural and cultivated grasses. The correlation coefficient ranged from 0.38 to 0.58, the correlation strength was average. With the use of correlation analysis nitrogen fertilizers were found to increase the specific activity of Cs-137 in airdry grass mass, the correlation strength depends on calendar years of the study, it may be strong and average. Adding potassium fertilizer into soil negate the negative effect of nitrogen fertilizers. The use of radioactive floodplains as hay fields without the use of agrochemical measures is unacceptable. According to made calculations, the use of coarse fodder grown on radiation contaminated lands leads to milk contaminated with Cs-137 content that exceeds the limit established by standard.