Potassium fixation and release characteristics of some benchmark soil series under rice-wheat cropping system in the Indo-Gangetic Plains of northwestern India

Potassium (K) fixation and release in soil are important issues in long-term sustainability of a cropping system. Fixation and release behavior of potassium were studied in the surface and subsurface horizons in five benchmark soil series, viz. Dhar, Gurdaspur, Naura, Ladowal, and Nabha, under rice-wheat cropping system in the Indo-Gangetic plains of India. Potassium fixation was noted by adding six rates of K varying from 0 to 500 mg kg(-1) soil in plastic beaker,,; while K release characteristics were studied by repeated extractions with 1 M HNO3 and 1 M NH4OAc extractants. The initial status of K was satisfactory to adequate. Potassium fixation of added K increased with the rate of added K irrespective of soil mineralogy and soil depth. Soils rich in K (Ladowal and Nabha) fixed lower amounts (18-42%) of added K as compared to Gurdaspur, Dhar, and Naura (44.6-86.4%) soils low in K. The unit fertilizer requirement for unit increase in available K was more in low-K soils. The study highlights the need for more studies on K fixation in relation to the associated minerals in a particular soil. Potassium-release parameters such as total extractable K, total step K, and CR-K varied widely in different soil series, indicating wide variation in the K-supplying capacity of these soils. K released with I M NH4OAc extractant was 20-33% of that obtained with I M HNO3. Total extractable K using 1 M HNO3 varied from 213 to 528 mg kg(-1) and NH4OAc-extractable K ranged from 71 to 312 mg kg(-1) soil in surface and subsurface layers of different soil series. The Ladowal and Nabha series showed higher rates of K release than Gurdaspur, Dhar, and Naura series, indicating their greater K-supplying capacity.