Changes occurring during a year in the soluble phosphorus and potassium in soil under crops in rotation experiments at Rothamsted, Woburn and Saxmundham

From May 1963 to April 1964 seasonal changes in soluble nutrients were followed in soil samples taken monthly from plots having none, PK, and NPK fertilizers in experiments at Rothamsted and Woburn. Phosphorus, potassium and magnesium concentrations in equilibrium extracts of the soils made with 0.0lM-CaCl 2 solution were determined. Exchangeable P was determined with an anion exchange resin. Samples were taken under five arable crops growing in rotation, and under permanent grass on the two soils.