128 



THE EOTHAMSTED EXPERIMENTS. 



average annual yield of nitrogen per acre of 15 lb., and the 

 clover gave, over much the same period, an average of 32 lb. 

 of nitrogen. 



TABLE 42. — Estimated yield of Nitrogen per acre, in lb., in Wheat 

 alternated with fallow, and in various leguminous crops, 

 without Nitrogenous Manure. 



PRELIMINARY PERIOD— Wheat and Fallow, 27 years, 1851-77 ; 

 Red Clover, &c, 29 years, 1849-77. 



Average per acre per annum 



lb. 

 32 



EXPERIMENTAL PERIOD. 



8 years only, 1878-85. 



2 12 years only, 1878- 



Yield of Against these amounts the various crops yielded, over the 



w^ro^CTi by subsequent years, averages per acre per annum as follows : 

 crops. The fallow-wheat, over 14 years 12 lb. ; the red clover (Tri- 

 folium pratense), over 8 years 14 lb. ; the white clover (Tri- 

 folium repens), over 12 years 24 lb. ; the vetch (Vicia sativa), 

 over 14 years 75 lb. ; the Bokhara clover (Melilotus leucantha), 

 over 12 years 58 lb. ; and the lucerne (Medicago sativa), over 

 12 years 137 lb. 



Or if we take the average amounts over the years of 

 actual crop only, they were — in the wheat 12 lb., in the red 



