The effects on lettuce of 5 rates of Nitrochalk and 2 rates of a PK compound fertilizer, all applied as base dressings, were examined during 1969 in 21 factorial experiments carried out on farms in different parts of England and Wales. The results did not justify any change in the standard ऩ and K recommendations for soils of average PK status, although it appears to be important to maintain levels in the soil that would avoid the necessity of making heavy dressings which could injure the crop. The optimal N rate was determined largely by rainfall. Dry conditions after sowing could result in N fertilizer causing stand losses and growth depression, and this restricted the optimum dressing to 40 kg/ha or less. Higher rainfall, resulting in drainage through the soil, increased the optimum rate.