178 THE LIVING ORGANISMS OF THE SOIL [chap. 



that supplied only when wheat was grown, but became 

 progressively greater the more frequently leguminous 

 crops occupied the ground. 



At Rothamsted the following average quantities of 

 nitrogen were removed per acre per annum in the 

 crop, when mineral manures only were applied : — 



Wheat (24 years) • • • • 22-1 



Barley (24 years) • • • • 224 



Roots (30 years) • . . • 16*4 



Beans (24 years, only 21 years in Beans) • 45*5 



Red Clover (22 years, only 6 years Clover) • 39*8 



In this case also the amount of nitrogen in the 

 produce was much increased when a leguminous crop 

 was grown. 



Another of the Rothamsted experiments showed still 

 more strikingly the accumulation of nitrogen by a 

 leguminous crop. A piece of land which had been 

 cropped for five years by cereals, without any nitro- 

 genous manure, v/as divided into two portions in 1872, 

 one being sown with barley alone, and the other with 

 clover in the barley. In 1873 barley was again grown 

 on the one portion, but the clover on the other, three 

 cuttings of clover being obtained. Finally, in 1874, 

 barley was grown on both portions. The quantities of 

 nitrogen removed in the crops of 1873 an d 1874 are 

 shown in the table. 



Thus, the barley which followed clover obtained 

 30-3 lbs. more nitrogen than the barley following barley 

 though the previous clover crop had removed H4lba 

 more nitrogen than the first barley crop. An analysis 



