A LONG-TERM STUDY OF SELENATE SORPTION IN FINNISH CULTIVATED SOILS

The behaviour of added selenate was investigated in a long-term study with 18 cultivated Finnish soils in vitro. In addition to the physico- chemical properties of the soils, the aerobic activity, measured as th e production of carbon dioxide, was taken as an independent variable. In an incubation experiment the selenium sorption of 16 quadruple soil samples was successful. According to the behaviour of selenate four g roups of soils were identified as follows: (1) where the sorbed fracti on increased during the whole experimental period (three soils); (2) w here the sorbed fraction increased during the first 15 days, remained stable or decreased up to 77 days and increased afterwards (five soils ); (3) where the sorption took place in 15 first days and no changes w ere found thereafter (six soils); (4) where almost all added selenate was first sorbed by 77 days, but half of it was soluble again at 161 d ays (two soils). During the first 2 weeks after the addition of selena te into the soils, chemical factors seemed to be the most important fa ctors determining the selenium retention; later on, however, soil micr obiological activity appeared to determine the fate of the sorped frac tion.