The present investigation was carried out at Tirhut College of Agriculture, Dholi an unique campus of Dr. Rajendra Prasad Central Agricultural University, Pusa, Samastipur, Bihar in year 2016-2017. Soils of North Bihar extending between 88°17'17.04" E to 83°54'18.02" E longitude and 27°17'4.44" N to 25°29'58.17" N latitude having a vast area of 52,925 sq. km.

The soils developed by sediments deposit of Gandak, Budhi Gandak and Bagmati rivers are calcareous in nature, whereas the soils developed by sediments deposit of Kosi, Adhwara group and Kamala Balan rivers are non-calcareous in nature. One hundred twenty-one samples were collected.

Wide variation in water soluble K (3.5 ppm to 67 ppm), exchangeable K (12 ppm to 274 ppm), available K (17 ppm to 330 ppm), non-exchangeable K (65 ppm to 2101 ppm), nitric acid soluble K (126 ppm to 2431 ppm) and total K (469 ppm to 22471.20 ppm) were recorded in soils of North Bihar and are present in following order viz. total K > nitric acid soluble K > non-exchangeable K > available K > exchangeable K > water soluble K.

Significant correlation and regression were found among various soil properties and pools of K. Correlation coefficient with organic carbon and pools of K (Available K, Nitric acid soluble K and Non-exchangeable K) are significantly and positively correlated (r = 0.186*, r = 0.201* and r = 0.182*, respectively) in North Bihar. Non-exchangeable K is significantly and negatively correlated with soil pH (r = - 0.225*). Nitric acid soluble K was significantly and negatively correlated with pH (r = - 0.237**) and cation exchange capacity (r = - 0.253**); non-exchangeable Potassium was significantly and negatively correlated with cation exchange capacity (r = - 0.271**).