Potassium fertilization and 137Cs transfer from soil to grass and barley in Sweden after the Chernobyl fallout

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Fertilization of soils contaminated by radionuclides with potassium (K) and its effect on 137Cs transfer from soil to crops is well studied in field conditions; however experiments over many years are few.The effects of potassium fertilization on cesium-137 (137Cs) transfer to hay, pasture grass, and barley growing on organic rich soils and mineral sand and loam soils in a number of field experimental sites situated in different environments in Sweden are summarized and discussed. The basic experimental treatments were control (no K fertilizers were applied), 50, 100, and 200 kg K ha−1. In the experiment, which lasted over 3–6 years, 137Cs transfer factors in control treatments ranged between 0.0004 m2 kg−1 (barley grain on sand soil) and 0.07 m2 kg−1 (pasture grass on organic rich soil). Potassium application on soils with low clay content i.e. mineral sand and organic rich soils was effective at the 50–100 kg ha−1 level. Application of 200 kg K ha−1 resulted in a five-fold reduction in 137Cs transfer for hay and up to four-fold for barley grain. The effects of potassium application were generally greater on sand than organic rich soil and were observed already in the first cut. After K application, the reduction in 137Cs transfer to crops was correlated with 137Cs:K ratios in plant material. Additional application of zeolite caused a 1.4 reduction of 137Cs transfer to hay on sand and 1.8-fold reduction on organic rich soil; whereas, application of potash-magnesia and CaO had no effect.