Soil applications of slaked lime and organic fertilizer for reducing ⁹⁹Tc transfer soil to rice seeds

To see if slaked lime and organic fertilizer applications to soil are useful as countermeasures for reducing ⁹⁹Tc concentrations in rice seeds after ⁹⁹Tc contamination of paddy fields, pot experiments were performed for two different paddy soils in a greenhouse. The upper soils for a depth of about 20 cm were treated with the agricultural materials and ⁹⁹Tc 15 d before transplanting. The effects were compared using the transfer factor (TF) defined as the ratio of the plant concentration to the soil concentration. In the case of control plants, TF values for brown rice in the two soils were 4.1 X 10^-4 and 4.3 X 10^-4. Of various types of the application, only the application of slaked lime at a lower dose (about 0.6 kg m^-2), which led to a 60% reduction in the TF value for one soil, seemed to be worth using as a countermeasure. Little effect of the same application was found in the other soil so it is important to determine the effect averaged for a number of soils. Organic fertilizer applications at both of two different doses increased the TF value. It is considered necessary to perform experiments for slake lime applications at doses lower than the above.