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Aims: In Alfisols, potassium (K) deficiency limits productivity, as these soils are poor in K-bearing minerals such as mica. As nutrient management practices greatly influence K nutrition of crops especially in the longer term, we evaluated the effects of 27 (1978-2004) years of cropping fingermillet ( Eleusine coracana G.) under different manure and mineral fertilizer treatments on K release, balance and yield sustainability on K deficient Alfisols in the semi-arid tropical region of southern India. Methods: Fingermillet (variety: PR-202) was grown each year under rainfed conditions with 5 different nutrient management treatments: control (no amendment), 10 Mg ha farm yard manure (FYM), 10 Mg ha FYM +50 % NPK, 10 Mg ha FYM +100 % NPK and 100 % NPK. Potassium release characteristics in the soil profile were determined using 1 N boiling HNO (strong extracting solution), 0.01 M HCl (medium extracting solution) and 0.01 M CaCl (mild extracting solution). Results: Continuous cropping of Alfisols for 27 years resulted in a decrease in K supplying capacity due to soil K depletion through crop K uptake. In soils without K addition, inherent soil supply could not meet the K requirement of fingermillet; thus, a negative K balance following 27 years of cropping affected K nutrition of the crop in all the treatments. As a result, the highest sustainable yield index (SYI) was observed using an integrated nutrient supply (combined application of nutrients from organic and inorganic sources), and the lowest index was obtained without K additions. Conclusion: For balanced nutrient management in cereal production systems, K nutrition needs urgent attention in the K deficient Alfisol region of southern India. Addition of any amount of organic manures available at field level offers an alternative strategy for maintaining soil K fertility to improve and sustain crop productivity. [ABSTRACT FROM AUTHOR]

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−1was 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. [ABSTRACT FROM AUTHOR]

Batch experiments were employed to examine the influence of oxalic acid on release kinetics of potassium (K) from soils along with adsorption and desorption of soil K+. The soils used were three rice soils from high-, mid-, and low-altitude zones. The results showed that soil K extracted using 0.2 mol L–1 oxalic acid was similar to that of 1 mol L–1 boiling nitric acid (HNO3). The relation between K release (y) and concentrations of oxalic acid (c) could be best described as y = a + b log c, whereas the best-fit kinetic equation of K release was y = a + b √t. The K release for soils was in the order Bonbagh > Ganasthan > Kreeri. An oxalic acid solution with low pH was able to release more K. Oxalic acid decreased soil K+ adsorption and increased desorption, the effect of which tended to be greater at lower pH. [ABSTRACT FROM AUTHOR]