RESIDUES OF AMMONIA SALTS 65 



In the wheat field at Woburn no practical effect is produced 

 by any residue of nitrate of soda applied to the preceding crop. 

 When, however, the larger quantity of ammonia salts is made 

 to alternate on the two halves of plot 8, a very distinct effect 

 is obtained from the residue of the ammonia salts put on the 

 preceding year. The increase obtained from the ammonia 

 salts amounts, on an average of eleven years, to 24-1 bushels 

 of wheat in the first year of their application, and to 5-2 

 bushels in the following year. The value of the residue was 

 thus 17-8 per cent, of the whole effect of the manure. 



In the Rothamsted barley field, a residue of ammonia salts 

 has produced a distinct though not large effect on the following 

 crop. A series of plots had for six years received annually 

 400 Ibs. of ammonia salts per acre, the dressing was then 

 reduced to 200 Ibs. By comparing the produce of the first 

 year with the reduced manuring, with that given in the same 

 season by plots which had received 200 Ibs. of ammonia salts 

 from the beginning, we find on plots 2AA and 4AA an excess 

 of produce amounting to 5 bushels of barley, chiefly due 

 apparently to a residue of the manuring previously applied. 

 That this excess was due to a residue of nitrates in the soil 

 is made more probable by the fact that plots i AA and 3 AA 

 showed a still greater excess of produce 8 and 6 bushels 

 respectively and on these plots a greater amount of unused 

 nitrates should have been present, owing to the absence of 

 phosphates in the manure, and the smaller produce per acre. 



In the Woburn barley experiments the effects produced by 

 residues from the larger dressings both of nitrate of soda and 

 ammonia salts become quite considerable. On the alternating 

 plots 8 and 9, 20-7 per cent, of the effect of the nitrate of soda 

 appears, on an average of eleven years, in the season after its 

 application, and 26-8 per cent, of the effect of the ammonia 

 salts. The amount of residue is much the greatest after a dry 

 season, which has retarded the nitrification and distribution of 

 the nitrogen of the ammonia. 



The facts now mentioned show a greater effect of residues 

 from ammonia salts than of residues from nitrate of soda ; a 

 greater amount of residue in barley than in wheat culture ; 



