Quantification of biological removal of <sup>137</sup>Cs from soil by above-ground part of bluegrass herbs following mineral fertilization
The article reported herein considers factors affecting the rate of transpiration of crops and reduction of 137Cs specific activity in the above-ground part of bluegrass herbs as fertilization of soil. Obtained results are best suited for moist soils. Due to mineral fertilization of the alluvial meadow sandy soil the quality of the fodder meet requirements of Veterinary rules and standards, VP 13-5-13/06-01. In regard to efficiency to reduce removal of 137Cs together with 1 t of moisture in the first and second hay crops of bluegrass herbs different fertilizers are arranged as follows: P60K60 > P60K45 > N45P60K75 > N45P60K60 > N60P60K45 > N60P60K90 > N60P60K75 > N60P60K60,where P is phosphorus, N - nitrogen, K - potassium. It is found that the removal of 137Cs from herbs depends not only on a potassium concentration in a fertilizer and sufficiency of nitrogen, but also on nitrogen/potassium ratio. Deficiency of potassium in a fertilizer, which is needed for synthesis of organic substances in a plant, is compensated by 137Cs ions. To reduce 137Cs specific activity in the fodder to the lower level of permissible limit of 400 Bq/kg, the potassium/nitrogen ratio in a mineral fertilizer should be higher than 1.5, providing that concentration of nitrogen in alluvial meadow sandy soils of high density contamination with radionuclides. The equation of biological removal of 137Cs by the above-ground part of bluegrass herbs establishes the relation between the radionuclide specific activity in the fodder and transpiration of crops of bluegrass herbs. The equation allows one to select soils on which the biological removal of 137Cs from herbs will be the lowest. This problem can be solved with the availability of cartograms of fields with indication of soil hydrologic constants.