EXPERIMENTS AT ROTHAMSTED 57 



in Hoos Field, it still remains 9 or 10 bushels per cwt. of 

 sulphate. I venture to think that the much better resul 

 obtained from ammonia in the barley field than in the wheat 

 field, is largely due to the different mode of applying the salt in 

 these two experiments ; and also to the fact that the wheat field 

 has drain-pipes through which nitrates may be lost, while the 

 barley field is provided with no artificial drainage. The mode 

 of applying the ammonia salts in the barley field seems on the 

 whole the best which can be employed to secure a full utilisation 

 of the ammonia. The ammonia salts are spread on the land 

 at the end of February, or beginning of March, and at once 

 ploughed in. Loss by volatilisation is thus as far as possible 

 prevented, as the salt is at once covered with the soil, while 

 the conditions necessary for nitrification are certainly supplied 

 even if dry weather should follow. In the wheat field the 

 ammonia salts are either applied before wheat sowing in autumn, 

 and are then liable to loss from autumn and winter drainage ; 

 or they are applied as a simple top-dressing in the middle of 

 March, when the salt lies on the surface, waiting for some 

 shower to carry it into the soil. Under these circum- 

 stances some loss by volatilisation may occur, and nitrification 

 and distribution may be unduly delayed in a dry season. 



From the consideration just urged it would seem that spring 

 corn is a crop especially adapted for the economic use of 

 sulphate of ammonia. 



In Table XIII we have only mentioned the results yielded 

 by 200 Ibs. of ammonia salts. In the first six years of the 

 experiment a whole series of plots received 400 Ibs. of ammonia 

 salts per acre. This heavier dressing of ammonia was clearly 

 excessive, the crop was generally more or less laid, and the 

 return per unit of ammonia was much less than that yielded 

 by the smaller application. It will be recollected that in the 

 wheat field the 400 Ibs. of ammonia salts yielded a return equal 

 to that given by 200 Ibs. What is the reason of this difference 

 between wheat and barley ? It is determined in part by the 

 essential difference in the tillage adopted for these two crops. 

 If the same soil is cropped with wheat and barley, the spring 

 tillage employed for the latter crop renders available for 



X*' 



