Potassium forms in relation to clay mineralogy and other soil properties in different agro-ecological sub-regions of northern India

The distribution of potassium (K) forms, their inter-relationship and relation with soil properties and clay mineralogy was studied in soils under different agro-ecological sub-regions of Punjab. Surface (0–30 cm) soil samples were analyzed for physico-chemical properties, soil mineralogy and K forms. The XRD analyses showed that quartz was the dominant mineral in coarse fractions followed by feldspar and mica, and illite in clay fraction. Water soluble, exchangeable and non-exchangeable K contents were higher in soils of south-western alluvial plain region compared to other regions. Readily available (water soluble + exchangeable) and non-exchangeable K constituted 0.02–0.07 and 0.1–0.9% of total K in soils, respectively. Mineral K constituted about 92–97% of total K with content ranged between 27.6–54.5 cmol kg−1. High values of total K were mainly due to the presence of high amounts of K-bearing minerals. Positive correlations were observed between K forms indicating the existence of dynamic equilibrium between these forms.