EXPERIMENTS AT ROTHAMSTED 55 



The addition of 200 Ibs. of mixed ammonia salts to the 

 superphosphate, or to the superphosphate and alkalies, is seen 

 to increase the produce of barley by an average of 21 bushels. 



During the first twenty years the produce of barley by 

 200 Ibs. of ammonia salts and phosphates was fully maintained, 

 and practically equal to that given during the same period by 

 an annual application of 14 tons of farmyard manure. In 

 the second twenty years there is a distinct falling off in 

 the produce by the ammonia salts. The falling off is naturally 

 greatest where no ash constituents have been supplied w r ith the 

 ammonia (plot IA), and is least where a full supply of these 

 ash constituents has been regularly given (plot 4A). 



Return per unit of Ammonia. If we deduct the pro- 

 duce of the unmanured plot from that given by the ammonia 

 salts alone (plot IA), and deduct the produce by superphos- 

 phate from that given by superphosphate and ammonia salts 

 (plot 2A), and further deduct the produce by superphosphate 

 and alkalies from that given by similar manure with ammonia 

 salts (plot 4A), we obtain the increase of crop apparently yielded 

 by the use of ammonia. In two columns at the right hand 

 of Table XIII., will be found the average increase yielded on 

 each plot for i cwt. of sulphate of ammonia applied. Where 

 the ammonia salt has been used alone, the average return has 

 been 6-7 bushels of barley for i cwt. of sulphate of ammonia. 

 Where superphosphate has been regularly applied with the 

 ammonia, the return is greatly increased, amounting to 11*2 

 bushels per cwt. of ammonia salt. Where the sulphates of 

 potash, soda, and magnesia, have been added to the super- 

 phosphate, the average return from the sulphate of ammonia 

 is slightly further increased, being now 11-3 bushels. 



The excellence of the return yielded by the ammonia salts 

 in the Rothamsted barley field is at once evident, the return is 

 in fact far better than that obtained in the adjoining wheat 

 field. On plot 6, in the wheat field, receiving 200 Ibs. of 

 ammonia salts with ash constituents, the return is only about 

 40 per cent of that theoretically possible if the whole of the 

 nitrogen of the ammonia had been assimilated by the wheat 

 crop. On plot 4A of the barley field, receiving exactly the 



