The classification and mapping of potassium reserves in soils of England and Wales

Potassium was extracted from samples of 21 surface soils and nine subsoils using a calcium-saturated cation exchange resin and concentrated HCI under reflux. Most of the important arable soils of England and Wales were represented in the samples. The two methods permitted determination of the amounts and rates of release of exchangeable K, K fixed in the weathered periphery of vermiculitic and illitic minerals, and K in the unweathered core of mica minerals. Potassium reserves in the soils were classified as High, Medium or Low according to the rate of release of fixed K and the amount and rate of release of mica K. The K reserves of soils in England and Wales could be mapped by soil series using this method of classification. Such mapping would provide data on the extent and availability of reserves in both the short term (i.e. to a crop over a growing season) and long term.