ASSESSMENT OF POTASSIUM RELEASE RATE FROM SOILS AND MINERALS USING POTASSIUM-SPECIFIC MANGANESE OXIDE ADSORBENT

抄録

Assessing the rate of release of potassium (K) from soils and minerals is important in soil management as well as in understanding weathering processes of minerals including micas and feldspars. We here propose a method to measure K release and transport rates in soils and minerals. The method uses an H-exchanged cryptomelane that is highly specific to K⁺ as an adsorbent. A small amount of sample wetted by water or aqueous solution is brought to contact with the adsorbent across two sheets of membrane filter and the amount of K accumulated in the adsorbent is measured after digestion. Test application of this method to four soil samples showed that an amount of K equivalent to exchangeable K migrated to the adsorbent within 24 h and further K release continued in 360 h or more at a rate depending on the type of soil. We also present an improved method for the preparation of the adsorbent.