Assessment of Potassium Fractions in the Northern Laterite Soils of Kerala: Mediated by Influence of Potassium Solubilising Fungi and Insoluble Potassium Sources

Abstract

Potassium (K) deficiency is a major constrain in the highly weathered and leached laterite soils of Kerala developed under humid tropics which limit the release of readily available K. Soil samples were collected from ten representative locations of northern laterites to understand the distribution of K fractions and to identify the soil having highest non available K reserves. Available K values ranged between 68.32- 425.04 kg ha-1, water soluble K value from 13.88-85.568 kg ha-1, exchangeable K from 51.408-339.472 kg ha-1 and the non- exchangeable K (nitric acid soluble K) ranged between 27.104-138.208 kgha-1 with the highest non-exchangeable K observed from Madikkai region. The predominance of nitric acid soluble K indicated the presence of a substantial amount of reserve K in the soil. An incubation study was conducted using the soil having highest non-exchangeable K to assess the solubilization potential of K solubilizing fungus: Piriformospora indica along with insoluble sources such as mica and feldspar. The treatments including T1 - soil alone, T2 - Soil + P. indica, T3 - Soil + P. indica + mica, T4 – Soil+ P. indica + feldspar. From the results it was evident that the treatments containing mica and feldspar in combination with P. indica demonstrated a consistent and significant increase in the readily available K fractions and in the soil solution. Enhanced mobilization of non-exchangeable K along with mineral amendment treatments, confirmed the dissolution of non-exchangeable K reserves through the production of organic and inorganic acids mediated by the fungus P. indica.