Vertical Distribution and Physicochemical Form of Fallout ¹³⁷Cs in an Allophanic Andisol Acidified by Long-term Fertilizer Application

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Samples were collected from an allophonic Andisol which had a history of the application of fertilizers for more than 60 years, and the vertical distribution and physicochemical form of fallout ¹³⁷Cs were determined. The pH values of the 1:10 water extract in the surface layer soils were 4.1, 4.7 and 6.2 for three different fertilizer treatments: chemical fertilizers only (F), F and compost (FC), and FC and lime (FCL), respectively. The concentration of ¹³⁷Cs at a soil depth of 0-25 cm showed a constant value and then sharply decreased. Below 40 cm, ¹³⁷Cs was not detected in any of the plots. The percentage distribution of ¹³⁷Cs in the exchangeable, organically bound, and strongly bound (residue) fraction was 17, 33 and 50%, respectively, and the physicochemical forms in the surface soil were not different among the three plots. This showed that the ¹³⁷Cs deposited in the agricultural fields was well mixed in the surface soil layers because of plowing, and the distribution of its physicochemical forms in the soil was similar after the long-term application of fertilizers even with soil acidification.