Radiocesium transfer from soil is lower in tall fescue than orchardgrass under conditions of lower soil exchangeable potassium

In Japan, additional potassium fertilization is used as a countermeasure for radiocesium-contaminated grasslands in the Tohoku and North Kanto regions. A 2-year pot experiment was conducted to assess the efficacy of using tall fescue (Festuca arundinacea Schreb.), a low-cesium-absorption grass species, to replace orchardgrass (Dactylis glomerata L.), the most common forage grass species in these regions, to reduce potassium fertilization and improve the forage mineral balance. The treatments were a combination of two grass species (tall fescue and orchardgrass) and two potassium application rates (0 [K0] and three times the conventional amount [K3]) with four replications. The grass species and potassium application rate had significant (p < .001) effects on plant cesium-137 concentrations. The results of the generalized linear mixed-model analysis indicated that when tall fescue replaced orchardgrass, cesium-137 in the forage grass was reduced to 34% and that the K3 treatment reduced cesium-137 to 46% relative to the K0 treatment. The difference in cesium-137 concentration between the two grass species increased as the soil exchangeable K₂O content decreased. The equations for estimating the cesium-137 concentration (y [g/kg]) from the exchangeable K₂O content (x [g/kg]) were obtained as y = 63.7e^–2.095x for tall fescue and y = 185.5e^–3.327x for orchardgrass. These equations indicate that tall fescue cultivation can reduce the risk of elevated radioactive Cs in the grass by reducing potassium fertilizer to approximately half that of orchardgrass. There were no differences in the response of plant potassium concentrations or the potassium/(calcium + magnesium) equivalent ratio to soil exchangeable K₂O content among the grass species. However, the mineral balance of forage can be improved by reducing potassium fertilizer applications for cesium-137 remediation. Tall fescue has good potential to remediate contaminated grasslands as it reduces additional potassium fertilization and improves the mineral balance of forage.