The e †ects of N fertiliser and poultry manure, applied to potato crops, on soil mineral N (SMN) after harvest and on the grain N o †take and yield (N off ) of subsequent unfertilised cereal crops, were measured at six sites in England during 1989È1994. At three sites of medium textured soil increased by N off between 0 and 49 kg ha~1 and grain yield by between 0 and 2É1 t ha~1, with increasing potato fertiliser N (PFN). The increases were greatest at applications of fertiliser N in excess of the optimum requirement for potatoes. No responses were found on two sandy and one shallow soil. Poultry manure applied in autumn or spring before the potatoes were planted increased by between 0 N off and 52 kg ha~1 and yield by between 0 and 2É1 t ha~1 at one site on medium textured soil but not on one of the two sandy soils. These results suggest that, at the rates of fertiliser N currently recommended for potatoes, the N requirement of subsequent cereal crops may be reduced by between 20 and 40 kg ha~1 on retentive soils but not on sandy and shallow soils. These reductions are less than currently recommended. However, the results also suggest that adjusting cereal fertiliser N according only to previous crop is unsatisfactory. The range of fertiliser N applied to potato crops in commercial practice is sufficiently great to signiÐcantly a †ect yield and hence the fertiliser N requirement of the sub-N off , sequent cereal crop.