Potassium requirement for

The study of all the forms of potassium in soils will no doubt be an important topic in the forthcoming volume on soil chemistry of the present encyclopedia. There have, however, been a reasonable number of laboratory studies on the extraction and availability of from feldspars and micas under varying conditions of temperature, pH and buffering, and over various particle-size ranges. A typical recent paper is that by Stohlberg [1959], and a recent summary of forms of potassium in the soil is that of Wiklander [1955]. The results of these studies can be very broadly summarized as follows. Potassium in feldspars is a major source of the potassium required for plant growth in many soils. It is, however, virtually nonexchangeable by comparison with the potassium in the micaceous clay minerals, and... 

---