Results are given of 124 factorial experiments testing N, P and K fertilizers for maincrop potatoes; the experiments were done by N.A.A.S. Soil Chemists in the years 1955–61. The experimental sites were in sixteen groups, corresponding to particular soil series or complexes.

There were substantial differences in mean yield and in response to the lower levels of P and K between soil series; the influence of soil was less at higher rates of application. Alternative methods of soil classification which appeared to be associated with response were texture, experiments on the lighter-textured soils showing higher responses to K; and depth of freely drained soil, soils with impeded drainage being associated with larger P responses. Responses to P and K were particularly large on soils in Wales and N.W. Cumberland.