ABSTRACT
Potassium and calcium are the two most abundant in the earth's crust. Potassium accounts for 2.6% of the earth's crust, and calcium 3.6%. The use of the term has been confusing and it is used here to refer to sedimentary mica that is heterogeneous and containing both no expanded and expanded minerals. Leaching losses and extent of K movement tend to increase as soils become more sandy. Wedge-zone fixation in field soils is little affected by normal changes in soil moisture and is highly dependent on K+ diffusion gradients. Experiments are conducted to determine the K fertilizer rate and to develop curves that relate crop yields to fertilizer rate for soils with varying soil test levels. Potassium fixation occurs in the interlayer space of 2:1 expanding layer silicate minerals. The weathering of illite and the release of K and its fixation parallel those for unweathered mica, weathered mica, and vermiculite.
