In a trial over three successive seasons, the yields of winter barley crops were mapped on a 6 ha field, the soils of which had been mapped according to a system of simple units corresponding to soil series as defined by the Soil Survey of England and Wales. Significant yield variation was explained by differences between soil map units, and the interaction with differences between seasons. The physical properties of the soil series and the potential soil moisture deficits in the three seasons suggested that moisture differences between the soils accounted for much of the observed differences in yield. The implications of these results for crop management in response to within-field variability are discussed.