30 CHARACTERISTICS OF AMMONIA SALTS 



such cases it is always the gramineous portion of the crop 

 that is benefited and not the leguminous. 



Sulphate of ammonia being a purely nitrogenous manure, 

 it also follows that it will frequently not produce its full effect 

 unless some of the other essential elements of plant food are 

 supplied with it. A purely nitrogenous manure can yield a 

 maximum return only when the soil contains a full supply of 

 phosphates, potash, lime, and the other essential ash consti- 

 tuents of plants. If the supply of these ash constituents in the 

 soil is deficient, sulphate of ammonia must fail to give a profitable 

 return, and may be entirely without effect. The application 

 of superphosphate, potash salts, or of other manures supplying 

 ash constituents, is thus often necessary if the ammonia salt is 

 to be used to advantage. The necessity for the simultaneous 

 use of other manures will be less when only small dressings of 

 ammonia salts are applied, and when they are only used occa- 

 sionally in the course of a rotation. The need for such 

 additions becomes greatest when large quantities of ammonia 

 salts are applied to the same land year after year. It is thus 

 in the long continued Rothamsted field experiments that we 

 find the most striking illustrations of the good effect of com- 

 bining phosphates and potash with ammonia, and of the very 

 inferior result given by ammonia salts when continuously 

 applied by themselves. Attention to the supply of lime, 

 alkalies, and phosphoric acid is more needed when ammonia 

 salts are systematically used than when nitrate of soda is 

 employed. 



We may now turn to the agricultural results obtained by 

 the application of sulphate of ammonia to crops. 



