The purpose of the experiment, described in this paper, is to examine the effect of pH on the fixation of applied K in clay minerals, namely, kaolinite, sericite, hydrated halloysite, montmorillonite. The clay minerals were adjusted to pH values ranging from 3.00 to 9.08, adding HCL or NaOH, and a constant level of KCL were added, and were dried and wetted alternately or stood at 30℃ for 48 hours. The results obtained were as follows :
1) As to kaolinite, there was no tendency in K-fixation influenced by the pH under moist condition or alternately dried and wetted conition.
2) As to hydrated halloysite, the amounts of fixed K showed the maximum at pH 5-6 under both conditions, and reduced at pH value below or above 5-6.
3) As to sericite, the amounts of fixed K increased as the pH value rose, in both conditions.
4) As to montmorillonite, the amounts of fixed K reduced as the pH rose, at pH value below 5.05, under alternately dried and wetted condition, and there was little deviation of the fixed K at pH value above 5.05.
Under moist condition, there was little deviation of the fixed K caused by pH.