| Abstract: | A balance sheet of potassium (K) was prepared in a long-term experiment that was started in 1985 on a loamy sand Udic Haplustept at the Potash Research Institute of India, Gurgaon, Haryana, India, involving a sorghum (fodder)–wheat cropping system. During the 20 cycles of sorghum and wheat, as much as 2,404 kg K ha?1 was released from the structural form of soil K that contributed 77.3% K to the total K removed by growing sorghum and wheat. However, this K released from the structural form could no longer sustain the growth of sorghum and wheat. Both water-soluble and exchangeable soil K forms contributed 3% K and nonexchangeable K contributed 6.6% K. Groundwater used in irrigation contributed 13.1% K. Potassium fertilizer is needed for the growth of sorghum and wheat on a loamy sand Udic Haplustept as in this long-term experiment and other representative soils both to sustain yield and maintain soil K fertility. |
