The purpose of these experiments reported in this paper is to determine the effect of calcium on the availability of the native potash and on the fixation of applied potash in the soil. The results are as follows :
(1) Fixed potash has been measured in two ways, namely aubmerged condition and upland farm condition (added 60% water of the water capacity). Fixed potash reduced slightly in the former condition, but greatly in the latter, with the increase of applied calcim.
(2) After the soil was dried and wetted repeatedly five times, water soluble and exchang eable potash were determined. It was noted that water soluble potash related to the fixation more greatly than exchangeable potash.
(3) It was recognized that fixed potash was increased by raising the pH of the soil with calcium hydroxide and decreased with sodium hydroxide.
(4) As fixed potash was investigated about the potash absorbed from the mixed solution of potash and calcium, in which the pH of the system was not appreciably altered, it was evident that the large excesses of calcium ions in the system would be more successful in competing with potash for the exchange positions, and hence a decrease in the amount of fixed potash should result.