Potassium Fractions and Release from Mineral Sources of Potassium as Influenced by Potassium Solubilizing Bacteria (Bacillus sporothermodurans)

Potassium (K) in soil exists in four different forms such as water soluble, available, exchangeable and non-exchangeable potassium. Variation in K fractions in soils through addition of different mineral sources of K is essential to determine suitable mineral source for crops. A laboratory incubation study was conducted using seven mineral sources of K such as sulphate of potash, langbeinite, sylvinite, kainite, patentkali, glauconite and rockdust for a period of 180 days to evaluate the release pattern of different K fractions with and without adding potassium solubilizing bacteria (Bacillus sporothermodurans). The results revealed that potassium fractions varied significantly with the mineral sources. The water soluble (86.00 kg ha-1 to 268.90 kg ha-1) and available K (144.60 kg ha-1 to 326.75 kg ha-1) were increased gradually while non-exchangeable potassium (59.95 kg ha-1 to 221.10 kg ha-1) showed a gradual decrease in content when potassium solubilizing bacteria added. But there was a corresponding decrease and increase in these fractions from 120 days of incubation when mineral sources alone were added. The highest water soluble and available potassium recorded in treatment received sulphate of potash and langbeinite with and without potassium solubilizing bacteria. The exchangeable K (45.20 kg ha-1 to 137.40 kg ha-1) recorded the highest content in treatment received sylvinite. HNO3 extractable K (353.80 kg ha-1 to 389.55 kg ha-1) was highest in treatment received sulphate of potash and only a slight variation was observed during incubation period. When analysing the release of K from mineral sources it can be concluded that sulphate of potash and langbeinite having more available form of K whereas sylvinite contain more K as exchangeable form. In rock dust and glauconite non-exchangeable form of K was dominating. Potassium solubilizing bacteria converted the non-exchangeable form to available form in all mineral sources of K.