Non-exchangeable potassium release and its removal in foot-hill soils of North-west Himalayas

In the present investigation, soils representing ten locations and three agro-climatic zones of foot-hills of north-west Himalayas were studied to assess Non-exchangeable Potassium (NEK) reserves, its release and influence of K-fixing capacity and clay minerals on NEK release. Maximum release of non-exchangeable K was obtained in temperate zone soils (295 mg kg^− 1) followed by intermediate zone (227 mg kg^− 1) and sub-tropical zone soils (106 mg kg^− 1), having relative soil quality index (RSQI) values of 85, 80 and 65, respectively. The quantitative analysis of clay minerals, through XRD technique, revealed that the temperate soils have more illite (averaging 62%) which holds well as a reason for high NEK reserves of 1556 mg kg^− 1 in these soils in comparison to intermediate (having illite averaging 53%) and sub-tropical (having illite averaging to 49%) soils having NEK amounting to 1022 and 918 mg kg^− 1, respectively. In order to study the NEK removal from the soils under investigation, maize was grown as a test crop and potassium was applied through four treatments having four levels of K (0, 15, 30 and 60 mg kg^− 1) applied as KCl. The crop demonstrated significant response in terms of dry matter yield up to 30 mg kg^− 1 in sub-tropical and intermediate soils while no such response was obtained in temperate soils. The percent NEK removed by maize crop from NEK reserves was 14, 25 and 20% in sub-tropical, intermediate and temperate soils, respectively. The information about NEK release, its removal as well as its relationship with K fixing capacity, clay minerals and RSQI can be used for understanding the K buffering potential of soils especially under adverse soil and climatic conditions that prevail in southwest India. Besides, the regression equations developed can be used for predicting NEK release on the basis of K fixing capacity and clay mineralogical composition.