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Potassium fixation was studied in four soil profiles under wet
and air—dry conditions. To determine the amount of potassium fixation KCI solutions with different concentrations were added to 5-g soil
samples in centrifuge tubes. The amount of extractable K was determined at different times. The amount of K fixed was taken as the amount
added to the test samples, plus that present in the controls (no K- added) ,minus the amount found in the extract (amounts per lOOg of
soil). The results indicated that there is a direct relationship
between the content in clay and illite and vermiculite and K fixation. Moreover, it was noticed that carbonate increases the amount of K fixed. K fixation is enhanced by the drying of the soil .The effect of the
level of K added, on the K fixation was illustrated such that as the amount of K added increased , the fixation increased until a maximum
is reached. Once the maximum is reached, further increase in the amount. of K added have little or no effect on the potassium fixation. This
indicated that these soils have a more or less limited capacity to fix
K. The relationship between the potassium fixation and level of K added (fixation curve) is parabolic. The rate of K fixation was highest
during the early hours of saturation and it gradually decreased and reached its minimum rate after 40 days. Potassium fixation represents 2.8 to 8 % of the CEC of clay minerals. Organic matter had no effect on potassium fixation in the soils studied.