J. M. NIWAS and C. B. DISSANAYAKE
Preliminary investigations of the K availability of some commonly occurring rocks of Sri Lanka
showed that granulitic gneiss, pink granite, migmatitic gneiss and microcline granite release relatively high
amounts of K indicating the capability of using these to provide K in plant nutrition. The finer crushed sizes
are more effective in releasing K, and the availability of the K-reserves under appropriate soil conditions
makes them possible substitutes for synthetic K fertilizers.