In order to describe the degree of within-field spatial variation of phosphorus, a spatial key indicator for P was developed. It was applied to data at two different geographical scales. In the first case, a general overview is given of the within-field phosphorus variability in central Sweden based on a very large number of soil analyses. In the second case, detailed data from nine project farms were compiled and specific examples are discussed in-depth. The economic potential of variable-rate P fertilisation is assessed. The examples show that the commonly used, traditional fertiliser recommendations lead to substantial over-application of phosphorus in parts of the fields. This, as well as the economic consequences, is visualised by the key indicator.