MODEL EXPERIMENTS ON THE POTASSIUM RELEAS E OF SOILS WITH HIGHER ELECTRIC CONDUCTIVITIES BY ELECTROULTRAFILTRATION (EUF)

For investigation on the effects of higher ion concentrations in soils on results of EUF (electro-ultrafiltration), performed at constant cu rrent, a light soil (12% clay) was analyzed by adding increasing amoun ts of a NaCl solution to the soil slurry in the EUF middle cell. Recor ding the course of voltage and current through the EUF cell, it was fo und that, 1) a continuous decrease of electrode voltage occurs over ex tended time periods, when the electric conductivity of the soil was in creased. 2) As a function of this voltage decline, the potassium conce ntration in the EUF-20 degrees C fraction was reduced, whereas in EUF- 80 degrees C fraction higher amounts of potassium could be found. 3) U nlike at very high levels of electric conductivity, the total K extrac tion by EUF was nearly unaffected, because losses in K content in the fraction EUF-20 degrees C could be compensated by the fraction EUF-80 degrees C. 4) According to Nemeth and Ziegler (1988) the ratio of EUF- K-80 degrees C to EUF-K-20 degrees C should be between 0.1 and 0.2 for light, but about 0.6 for heavy soils. Under the influence of higher e lectric conductivities this figure for light soils, however, approache d values for heavy soils. 5) Also, the contents of magnesium and calci um showed marked decreases at higher electric conductivities in the EU F-fractions a and b (= EUF-20 degrees C). Contrary to the total amount of extractable potassium, the total contents of magnesium and calcium , extractable by EUF, were markedly decreased by higher electric condu ctivities in the light soil. It is recommended, that the parameters vo ltage and current should be considered in interpretations of EUF-fract ions from soils with higher levels of electric conductivity.