Abstract: Biocycle and equilibrium of radioactive substances in different soils are studied in this paper. The results show that the content of radionuclides in soil profile decreases gradually along with genetic horizons. The biological accumulation coefficients of different nuclides range from 1.06 to 1.44, and the content of radioactive substances in different plants is in order of fodder grass>crop≥shrub≥fruit tree>arbor. The concentration coefficient of plants for α radioactivity is less than 0.10 and that for β radioactivity is 0.5-1.0. Three equilibrium types(accumulation, consumption and medium) of soil radioactivity under different land utilizations are put forward.

Key words: Soil radioactivity, Biocycle, arsenite, aging, available As, combined As.