LEGUMES FEED ON NITRATES 323 



the air. Now, nitrogen is required by the root for its growth as 

 well as for the growth above the ground, and we have every reason 

 for believing that the root also would obtain it in the same pro- 

 portion from air and soil as did the hay crop. 



Distribution of Nitrogen in Legumes. If we examine dry matter 

 and total nitrogen occurring in the roots and stalks of alfalfa, we 

 should be able to decide whether more nitrogen is being returned 

 to the soil in the roots and residues than is removed by the growing 

 plants. 



The results for this comparison have been obtained from Illinois 

 and Delaware experiments and are tabulated below: 



Dry matter Nitrogen Per cent, of 



per acre, per acre, total nitrogen, 



Legume. pounds. pounds. in tops. 

 Sweet clover: 



Tops 9029 174\ ?6 



Roots and residues 3748 54 / 



Crimson clover: 



Tops 4512 103 \ 70 



Roots 2022 41 / 



Alfalfa: 



Tops 2267 54. 8 \ 60 



Roots 1980 40. 4 / 



With the clover, three-fourths of the total nitrogen is found 

 in the plant above ground and only one-fourth in the roots, while 

 alfalfa shows a greater proportion in the roots 40 per cent. This 

 represents the proportion for the first-year growth for alfalfa and 

 it is not likely that in the older plant this proportion of the total 

 nitrogen would be maintained in the roots. Hence, it is quite 

 certain that if only two-thirds of the total nitrogen of the plant 

 is obtained from the air the quantity returned to the soil with the 

 roots and plant residues does not exceed that removed from the 

 soil by the growing plant, which would give no increase in soil 

 nitrogen from the growing of a legume where the entire crop is 

 removed, and this even where the roots are allowed to remain 

 and decay. Yet we find some farmers who remove the roots from 

 the soil and even then expect an increase in their soil fertility. 



Legumes Feed on Nitrates. It is, therefore, rather certain that 

 the legume, where the crop is harvested, does not increase the 

 soil nitrogen of the fertile soil of Illinois and other soil fairly rich 

 in nitrogen. But what will happen on the arid and semi-arid soil 

 where nitrogen in many cases is the limiting element and is present 

 in much smaller quantities than it is in the soils on which the 

 experiments considered have been conducted. Experiments which 

 have been conducted at the Utah Experiment Station during the 

 last twelve years have demonstrated that even on soils poor in 

 nitrogen the legume first feeds upon the combined nitrogen of the 

 soil. It is known that plant residues and other complex nitrogen 



