108 AGRICULTURE 



manure, 26*1 cwts. where about 3J ewts. of 

 ammonium salts were annually employed, 

 and 23'3 cwts. where about the same quantity 

 of superphosphate was used ; whereas from 

 the plot receiving both ammonia and super- 

 phosphate an average yield of 35*5 cwts. of 

 hay was annually obtained. These figures show 

 that phosphoric acid used alone in the form 

 of superphosphate has produced the quite 

 insignificant increase of one-tenth cwt. of hay, 

 and although nitrogen, in the form of am- 

 monium salts, similarly employed, has done 

 a little better, the increase over the un- 

 manured land is only 2*9 cwts. of hay per 

 acre. On the other hand, when super- 

 phosphate was added to ammonium salts 

 it was accountable for 9*4 cwts. of hay, and 

 when ammonium salts were added to super- 

 phosphate the yield of hay was increased by 

 12'2 cwts. The aggregate increase, in fact, 

 of these two substances used on separate 

 areas was only 3 cwts. of hay, but when 

 applied together to the same land they pro- 

 duced an increase of hay amounting to 12*3 

 cwts. These figures show that this land at 

 Rothamsted is deficient in both phosphoric 

 acid and nitrogen, so that when only one of 

 these substances is employed the increase 

 is quite insignificant, for the reason that it is 



