1. The problem of when to apply nitrogenous top-dressings to winter wheat has nover been satisfactorily solved. Detailed field and glasshouse experiments on the effects of nitrogenous manuring on the development of wheat plants, and a number of other experiments involving the nitrogenous manuring of wheat are described and the results discussed.

2. Partial regression coefficients of grain yield on individual components of yield are used to show how variable is the relationship between grain yield and the components of yield.

3. It is concluded that field experiments are never likely to determine an optimum time for nitrogen top-dressing because of the unpredictable relationships between individual yield components and grain yield, and because of the variation in response to nitrogen introduced by seasonal and environmental factors.