VII.] VALUE OF LEGUMINOUS CROPS 135 



wheat by first growing crops of vetches or lupins or 

 beans. In English agriculture the same idea was 

 enshrined in the Norfolk four-course rotation, in which 

 red clover or beans are followed by wheat ; and it was 

 well known to the practical man that the wheat always 

 flourished best where the clover had been good in the 

 previous year. Boussingault, who was the first scientific 

 man to make field experiments, drew up a kind of 

 balance-sheet in which the carbon and nitrogen sup- 

 plied to the land over a term of years was com- 

 pared with the amounts of the same elements 

 taken away in the crops. Of course, in all cases the 

 carbon removed was enormously in excess of that 

 supplied, because of the assimilation that had taken 

 place, but when the land was alternately bare fallowed 

 and cropped with wheat, there was no more nitrogen 

 obtained in the crop than had been put on in the manure. 

 But with other rotations including clover and beans, 

 there was always more nitrogen harvested than was 

 applied ; and when the land was occupied by lucerne or 

 alfalfa, more than a hundred pounds of nitrogen were 

 taken away annually for five years, and yet the soil 

 showed no sign of impoverishment, rather the contrary. 

 Another example of the same kind was obtained at 

 Rothamsted : in 1873 a piece of land was divided, one 

 part being cropped with barley, the other with clover 

 which had been sown the year before ; the nitrogen was 

 determined in the two crops, and showed that in the 

 barley 37 lb. of nitrogen was removed, in the clover 151 

 lb. In the following year the whole of the land was sown 

 with barley, and the crop where barley followed barley 

 contained 39 lb. of nitrogen per acre, whereas that which 

 followed clover contained 69 lb. per acre. An analysis 

 was also made of the soil in 1873, after the first barley 

 and clover crops had been removed, and the soil after 



