EFFECT OF K RELEASE AND FIXATION ON THE ION-EXCHANGE PROPERTIES OF ILLITE

Abstract

Quantity-intensity [Q/I] relations related the amount of immediately available K in a soil to its availability, as measured by the activity rate aK[square root]aCa in the soil solution. Previous studies had shown that the fall in the activity ratio, which followed the removal of K in crops, could be predicted from the Q/I relations, and that the form of Q/I relations was little affected by K-release or -fixation in amounts likely to be removed in crops over 5-15 years. The present work has shown that when very large amounts of inter-layer K are removed from illite, enough for 100 years of cropping, by sodium tetraphenyl boron, there are considerable changes in the form of the Q/I relation. These are similar to the differences between the Q/I relations of the K-depleted and K-fertilized plots of the 120-year Broadbalk trial. The evidence suggests that not only is a considerable extent of new exchange surface opened up, but also that the charge density on the new surfaces is lower than that on the former exchange surfaces, and/or that their specificity for K may be higher.