The soils from England, France and Poland having a range of organic matter contents were studied. The total contents of clay and organic matter are used to calculate the amounts of non-complexed clay and organic matter in the soils. Measurements of soil water retention are used to calculate the values of an index of soil physical quality, S*. It is shown that soils with larger contents of non-complexed clay have smaller values of S* whereas soils with larger contents of non-complexed organic matter have larger values of S*. We then use these values of S* in an existing model based on results from tillage experiments in the field to predict the amount of soil crumbling produced by mouldboard ploughing. It is predicted that soils with larger contents of organic matter will crumble into smaller aggregates (and fewer clods) when tilled. A new measure of non-complexed material, NCM, is introduced that enables different soils that are poor and rich in organic matter to be considered on the same scale.