Eleven winter wheat experiments were carried out from 1955–57, to compare the effects of nitrogen on three stiff-strawed varieties of winter wheat, Heine 7, Hybrid 46 and Minister. In 1955 the experiments tested ‘Nitro-Chalk’ top-dressings at rates supplying 0·45, 0·90 and 1·35 cwt. N/acre. In addition, drilled dressings supplying 0·15 cwt. N/acre were supplemented with either 0·30 or 0·75 cwt. N/acre as a top-dressing.

In the 1956 and 1957 experiments ‘Nitro-Chalk’ top-dressings were applied at 0·60 and 1·20 cwt. N/acre. In addition, divided dressings were compared by supplementing 0·15 cwt. N/acre by combine-drill with 0·45 cwt. N top-dressing.

Significant increases in yield were obtained from the first increment of nitrogen in twenty-three of the thirty-three available comparisons. There were significant additional gains from the second increment of nitrogen in only seven of the same comparisons. Responses to nitrogen varied considerably between seasons. Large and consistent responses were obtained at all centres in 1955 and dressings supplying 0·9 cwt. N/acre were well worthwhile. In 1956 responses were generally smaller and dressings in excess of 0·6 cwt. N/acre could only be justified at two centres. Mean responses in 1957 were lower than those obtained in either of the previous season and 0·6 cwt. N/acre was sufficient for maximum yields at three of the four centres.

There was little advantage in dividing dressings of nitrogen between autumn and spring in any of the experiments and none of the differences reached significance. On average, higher yields were obtained by retaining the whole of the nitrogen until the spring, than by applying part of the dressing in autumn by combine-drill.

Comparisons between the varieties show that Hybrid 46 was the only variety which was able to take consistent advantage of the heaviest rates of manuring. In each year Hybrid 46 produced the highest percentage increase in yield and Minister the lowest. In addition Hybrid 46 contained the highest percentage of nitrogen in the grain when averaged over each level of manuring. The percentage recovery of nitrogen was calculated for each year and each variety. Comparisons of this data show that Hybrid 46 converted more of the fertilizer nitrogen into grain or crude protein than either of the other two varieties. The experiments provide evidence that there are considerable variations in the efficiency with which present-day winter wheat varieties can utilize nitrogen, and that varieties with both high fertilizer efficiency and high unmanured yields are likely to increase the level of crop production.