EXPERIMENTS AT ROTHAMSTED 109 



many years at Rothamsted, and it appears that the propor- 

 tion of the nitrogen of the ammonia salts recovered in the crop 

 is quite as great when the ammonia salt is used with farmyard 

 manure as when the same salt is employed with only super- 

 phosphate and alkalies. The increase given by the ammonia 

 salts when used with dung is so much smaller, because the 

 produce of this manuring is more highly nitrogenous in com- 

 position, and the crop at harvest contains a very large propor- 

 tion of leaf. This delayed development of root is characteristic 

 of excessive nitrogenous manuring, the absence of a proper 

 supply of ash constituents, or of the deficiency of sunshine and 

 warmthv during the season of growth. 



Return per Unit of Ammonia. It will be seen from 

 Table XX^V (p. 107), that when the ammonia salts are used 

 to the greatest advantage, there is an apparent return of 

 nearly 2f tons of roots for i cwc. of sulphate of ammonia 

 employed.* The return from the ammonia greatly falls 

 off when the supply of ash constituents is deficient. It is 

 also considerably less when the ammonia salts are used 

 with a good dressing of farmyard manure, a result which is in 

 part due to the deficiency of potash in such a mixture. 



It will be observed that the proportion of leaf is smallest, 

 and of root greatest, when the ammonia is used with a full 

 supply of ash constituents ; any deficiency in these produces an 

 imperfectly developed crop including a large proportion of 

 leaves when harvested. 



Influence of Climate. The return obtained from the 

 manure varies much in different seasons. The crop can attain 

 to an enormous growth only when the circumstances in which 

 it develops include an adequate supply of rain and sunshine. 

 Examples of the results yielded by the manures already 

 mentioned when the season admits of a large growth will be 



* This figure is probably somewhat above the truth, as the plot re- 

 ceiving only superphosphate and alkali salts, the produce of which is 

 used to ascertain the increase by ammonia, is in a specially exhausted 

 condition, due to its long cultivation without nitrogenous manure, and the 

 exhaustion of soil nitrogen by spring and summer tillage. 



