Vol. 9, Special Issue 12, Part O (2025)

The investigation was carried out at Dr. Rajendra Prasad Central Agricultural University, Pusa, Bihar, to evaluate the spatial variation in different forms of potassium (K) in the soils of North Bihar. The study area extends between 83°54′18.02″ and 88°17′17.04″ E longitudes and 25°29′58.17″ and 27°17′4.44″ N latitudes, covering nearly 52,925 km². The soils of this region are primarily alluvial in nature—calcareous soils have developed from the sediments of the Gandak, Budhi Gandak, and Bagmati rivers. In contrast, non-calcareous soils originate from the alluvium deposited by the Kosi, Adhwara, and Kamala Balan rivers. A total of 121 representative soil samples were collected and analyzed to determine the content of water-soluble, exchangeable, non-exchangeable, and total potassium. The concentrations of these K fractions exhibited considerable variability, with water-soluble K ranging from 3.5 to 67 ppm, exchangeable K from 12 to 274 ppm, non-exchangeable K from 65 to 2101 ppm, and total K from 469 to 22,471 ppm. The dominance of different K forms followed the sequence: total K > non-exchangeable K > exchangeable K > water-soluble K. Distinct spatial variability in K distribution was observed among the districts, which may be attributed to variations in parent material, topography, and land management practices. The results highlight the need for site-specific potassium management strategies to promote efficient nutrient utilization and maintain soil fertility in the intensively cultivated areas of North Bihar.