ROTH AM 57 ED EXPERIMENTS 35 



bushels, and during the fourth ten years 33! bushels. That 

 the effect of the ammonia salts does not wear out is shown, 

 however, most strikingly by the produce of these three plots 

 in the excellent season of 1894, ^Y which time ammonia salts 

 had been applied to the land continuously for about 50 years. 

 The dressed corn yielded by plots 6, 7, and 8 in 1894 

 amounted to 38, 48^, and 49 bushels per acre. 



Return per Unit of Ammonia. The return given by 

 ammonia salts under various conditions is best seen by refer- 

 ing to the figures in the two columns at the right hand of the 

 table. We have here the increase in dressed corn and straw 

 for i cwt. of sulphate of ammonia applied. In this calculation, 

 and in all others of a similar character which follow, the sulphate 

 of ammonia is assumed to be of the best modern quality, 

 and to contain 25 per cent of ammonia, or 28 Ibs. per c\vt. :: 



It appears from the figures given that the smaller applica- 

 tion of 200 Ibs. of ammonia salts per acre, and the next 

 larger application of 400 Ibs., were both used with an equally 

 profitable result, the return being about 5 bushels of wheat, 

 and 5 cwts. of straw, per cwt. of sulphate of ammonia. When, 

 however, the quantity of ammonia salts is still further in- 

 creased, as on plot 8, although a larger crop is harvested, the 

 return in corn per unit of ammonia is diminished, while the 

 return in straw shows but little falling off. It is thus clear 

 that in the wheat field at Rothamsted, with a full supply of 

 phosphates and potash salts, dressings of sulphate of ammonia 

 up to 4 c\vts. per acre may be profitably applied, but that 6 cwts. 

 is an excessive quantity, and produces more straw than corn. 



A farmer will seldom, if ever, be able to employ so large a 

 dressing as is profitably applied in Broadbalk field. In Broad- 



*It has been already mentioned that the quality of the ammonia 

 salts employed at Rothamsted (and elsewhere) was many years ago 

 lower than it is at present. In calculating the return yielded by am- 

 monia in the 40 years, 1852-91 (Table V.), a middle value has been 

 assumed for the ammonia salts, namely 105 Ibs. of ammonia in 400 Ibs. of 

 the mixed salts. In Table VI., 400 Ibs. ammonia salts are taken as con- 

 taining 103-3 Ibs. f ammonia. In the Holkham and Rodmersham experi- 

 ments, which relate solely to an earlier period, the 400 Ibs. of salts are 

 taken as containing 100 Ibs. of ammonia. 



