Potassium In soils from selected plots of the Broadbalk Experiment at Rothamsted, and Rotation I experiment at Saxmundham, U.K. was measured by five methods: the boiling nitric acid extractions of Haylock and Maclean, electro-ultrafiltration, release to Ca-saturated ion exchange resin, and a new procedure using extraction by HC1 under reflux. All the methods showed clearly the differences between the two soil types, and between the differently fertilized plots on the basis of amounts, and in some cases rates of release, of different categories of soil K (exchangeable, fixed and native). The quantity of exchangeable K measured by each method, except that by Ca-resin, gave significant correlations with the K balance of the soils, and yield and/or K offtake of winter wheat grown on the plots. The new HC1-reflux method gave the closest correlations. The amount and rate of release of fixed (available but not exchangeable) K estimated by HC1-reflux was also correlated with yield and offtake.
- Potassium release
- soil analysis