16 



of ammonia in the experiments at Rothamsted and at outside 

 centres inspected by us were as follows : — 



1922 

 Rothamsted. 



1923 

 Rothamsted. 



1924 

 Rothamsted. Outside 

 Centres. 



Average of all Soils 



and Seasons to 



1920 



Wheat, bu. ... 

 Barley, bu. ... 

 Oats, bu. 

 Potatoes, cwt. 

 Swedes, cwt. 



3-25 

 5-5 



20 

 20 



4-5 

 8.3 



22-25 

 25 



8-16 



20 

 5-9 



4-3-6 

 3-5 



30 



4-5 

 6-5 



7 



20 



20 N. 

 10 S. 



Country 

 Country 



SIZE OF DRESSING AND TIME OF APPLICATION. 



The effect of doubling the nitrogenous dressing and supply- 

 ing 2 cwt. sulphate of ammonia per acre is to give a further 

 increase in crop. In the case of cereals this second increase is 

 not infrequently greater than the first, so that the effect of the 

 double dressing is to give more than double the increase obtained 

 from the single one. This was shown both in 1923 and 1924; 

 the yields per acre were : — 



No 

 Nitrogen. 



1 cwt. 

 Sulphate of 

 Ammonia. 



2 cwt. 

 Sulhpate of 

 Ammonia. 



Increment in Yield for 

 1st cwt. 2nd cwt. 



1923 Oats, bu ... 

 Straw, cwt. 



1924 Barley, bu. 



29-2 



19 



23-9 



37-3 



26 



32-5 



46-5 



36 



42-7 



8-1 



7 

 8-6 



9-2 

 10 

 10-2 



In the case of potatoes, however, the second increment in 

 yield is usually less than the first, though the total effect of the 

 higher dressing still remains profitable because of the higher 

 value of the potato crop. 



The results have been, in tons per acre : — 



1923 

 1924 



No 

 Nitrogen. 



120 



8-0 



11 cwt. 

 Sulphate of 

 Ammonia. 



13-7 

 9-5 



3 cwt. 

 Sulphate of 

 Ammonia. 



151 

 9-4 



41 cwt. 

 Sulphate of 

 Ammonia. 



14-8 



Increment in Yield for 



1st 2nd 3rd 



dose. dose. dose. 



1-7 

 1-5 



1-4 



Nil 



Nil 



The effect of the nitrogenous dressing depends on its time of 

 application. For cereals it has happened that the later dressings, 

 especially when large, have been more effective than the earlier 

 ones (p. 118). For potatoes it has hitherto always happened at 

 Rothamsted that the application of the sulphate of ammonia with 

 the seed has been more effective than the later top dressing when 

 the plants are showing through the ground. Swedes appear to 

 behave in the opposite way. The physiological basis of this 

 problem of nitrogen intake and nitrogenous efficiency is being 

 studied by Dr. Gregory. 



