Importance of Nitrogen to Growth of Plants. 239 



a lack of water-soluble nitrogen needed as plant-food and that the subse- 

 quent increased growth was due directly to the nitrogen applied and 

 that it served as plant-food? Does it not seem plausible that weeds by 

 taking up a portion of the small amount of nitrogen available just at the 

 critical period in the life of the maize plant or other plant which is 

 being cultivated, may cause the injury so commonly observed ? 



Factors influencing supply of water. 



It may be said that it is impossible that both the above plats should 

 show the same per cent, of moisture since the greater amount of vegeta- 

 tion must have required more moisture. It does not necessarily follow 

 that because a plant actually uses a larger amount of water that it dries 

 the soil more than one which uses a less amount. It would of course, 

 if the evaporation, the run off and the amount of drainage, remained the 

 same, but evidently they do not as the following incident will illustrate. 

 On June 13, Quiroga found in the surface foot, 26.9 per cent, of moisture. 

 During the next six days the rainfall was .28 of an inch. The largest 

 possible amount of moisture to be found in that soil at a depth of one 

 foot would be 29.6 assuming a cubic foot of soil to weigh 75 pounds. 

 The actual amount found was 25.6, or a difference of four per cent. 

 During the next 12 days the rainfall was i.ii inches. The largest 

 possible amount of moisture to be found was 35.6 inches; the actual 

 amount found was 27.4 or a difference of 8.2 per cent. Obviously, if 

 on a portion of this soil for other causes than the supply of moisture, 

 vegetation grew more vigorously it could use a part of the water which 

 would otherwise go to waste, and thus not necessarily reduce the per- 

 centage of moisture found in the soil. 



The importance of nitrogen in grozving alfalfa. 



Attention is next called to a series of observations on alfalfa as 

 illustrating the importance of nitrogen in growing crops. The Cornell 

 Station has published (Bui. 237) some experiments showing that on 

 Dunkirk clay loam three things are necessary to the successful culture 

 of alfalfa; lime, manure and inoculation. What do nodule bacteria do? 

 What does lime do? What does manure do? 



(i) What do nodule bacteria do? 



What are the characteristics of legumes? First, to produce a pro- 

 duct containing a high percentage of nitrogen. In the case of some of 

 our cultivated legumes, such as alfalfa, very large amounts are laid up in 

 the plant in a very short space of time. A second characteristic of 

 legumes is to bear nitrogen-gathering bacteria. Is this an accident? It 



