Severe alteration of clay minerals from an exhaustive soil potassium leaching experiment revealed a potential threat to the soil potassium availability in five major agricultural soils of India

Imbalanced soil potassium (K) management in Indian agriculture is threatening the K-bearing clay minerals that oversee the long-term K-supply in crop production. With 0.1 N BaCl 2 , a laboratory-based leaching experiment was conducted to exhaust K (90-time or 90 NOL) from five agriculturally important Indian soils: alkaline alluvial, acidic alluvial, calcareous alluvial, red, and black, to evaluate their post-depletion K-supplying behaviors. The entire leaching session underwent two phases: falling rate phase (1 22 NOL), and steady state phase (23 90 NOL). Zero-order kinetics (R 2 = 0.98–1.0) suggested that K-desorption was independent of residual soil-K, especially at steady state phase. The XRD revealed random interstratifications of clay minerals. A simultaneous decrease in illite-001/002 (2.63–1.12) suggested that trioctahedral illite governed the majority of soil K-loss. The cg shift from 11.85 Å to 15.65 Å in alkaline alluvial soil and 9.74 Å to 9.44 Å in red soil confirmed “smectitization” and “kaolinization”, respectively, indicating an irreversible alteration of 2:1 clay minerals. Nonexchangeable-K extracted by sodium tetraphenyl-borate {NEK NaTPB (1 h)} showed higher responsiveness (R 2 = 0.86–0.97) towards the soil-K depletion. Principal component analysis showed that enhanced K-fixation capacity and deterioration of NEK NaTPB (168 h) progressed parallelly and “vermiculitization” of trioctahedral illite facilitated the process. However, K-fixation paradox in those K-leached soils uncovered the irreversible nature of soil K release (71 91%). Depending upon the K-management practices, soils under dominant cropping systems might need nearly 14–31 years to exhaust the equivalent amount of soil-K as it was achieved in this study. • Steady state K release was independent of diverse nature of soil types. • Majority of nonexchangeable K (71–91%) release was irreversible in nature. • Severe loss of trioctahedral illite K facilitated smectitization and kaolinization. • NEK NaTPB (1 h) was most sensitive to severe soil K depletion.