170 



THE ROTHAMSTED EXPERIMENTS. 



Yield with- 

 out manure 

 exceeds 

 Ainerican 

 yield. 



Nitrogen 

 in the soil. 



Effect of 

 keeping 

 down 

 •weeds. 



the nitrogen supplied by it would be largely due to old 

 accumulations. 



Lastly in regard to the produce of wheat grown 

 so many years in succession without manure, it may be 

 observed that the average yield over 40 years, 1852-91, 

 was 13 bushels per acre per annum, which is more than 

 the average of the whole of the United States, including 

 their rich prairie lands ; indeed it is more than the average 

 yield per acre of the wheat lands of the whole world ! 

 That the result is not due to richness of soil will be 

 obvious from the fact that the percentage of nitrogen in 

 the dry sifted soil, exclusive of stones, from samples 

 taken in 1893, of every 9 inches of depth, down to 12 

 times 9, or to a total depth of 9 feet, was, for the respective 

 depths from the first to the twelfth, as follows: 0.1110, 

 0.0720, 0.0609, 0.0482, 0.0445, 0.0436, 0.0335, 0.0284, 0.0264, 

 0.0214, 0.0219, and 0.0251. 1 Thus, the percentage of nitrogen 

 in the surface-soil is considerably lower than in the average 

 of wheat-lands in Great Britain ; it is considerably less than 

 half as high as in the case of average permanent meadow- 

 land ; and it is only about one-third as high as published 

 analyses show in some Illinois prairie soils. The subsoils are 

 also very poor in nitrogen. It is further to be observed that 

 a full mineral manure, annually applied, gave less than f 

 bushel per acre per annum more than the unmanured plot. 

 Hence, it may be concluded that it was not owing to any 

 deficiency of mineral supply, but of nitrogen, that the limita- 

 tion of the produce was due. On the other hand, that with 

 a soil so poor in nitrogen the yield was nevertheless higher 

 than the average of the United States, or of the world at 

 large, is to be explained by the fact that great care is taken 

 to keep down weeds, which would otherwise appropriate a 

 large share of such fertility as the soil possessed. 



Farmyard Manure every year. 



In the application of farmyard manure every constituent 

 is supplied in excess. The highest yields of the series of 

 years were— 48£ bushels in 1891, 45* in 1894, 44 in 1863, 

 43 in 1890, 41£ in 1868, 41£ in 1857, 41£ in 1854, 40* in 

 1889, 40£ in 1885, and 40 bushels in 1864. The lowest 

 yields were— 16 bushels in 1879, 19£ in 1853, 20* in 1844, 

 23| in 1876, and 24£ in 1877. 



The average produce per acre per annum over the first 



1 It should be explained that these samples were not taken in our usual 

 series for analysis, but only from one place, specially to provide illustrative 

 specimens of the soil and subsoil to send to the Chicago Exhibition. 



