548 SOILS: PROPERTIES AND MANAGEMENT 



largely through bacterial activity. It may be stated with 

 certainty that one of the possible limiting factors to 

 crop growth is a lack of water-soluble nitrogen at critical 

 periods in amounts necessary for normal crop develop- 

 ment. Since soluble nitrogen may be very readily lost 

 from the soil by leaching, the problem of proper plant 

 nutrition becomes a serious one. Not only must the 

 farmer be able to so regulate its addition in fertilizers 

 as to obtain the highest efficiency, but he must understand 

 the control and encouragement of the natural fixation 

 as well. The emphasis placed on all phases of the nitrogen 

 problem serves to reveal its great importance in fertility 

 practices. 



Because of the immediately visible effect from the ap- 

 plication of soluble nitrogen, the average farmer is prone 

 to ascribe too much importance to its influence in proper 

 crop development. This attitude is unfortunate, since 

 nitrogen is the highest-priced constituent of ordinary 

 fertilizers. Moreover, of the three primary elements 

 it is the only one which added in excess will result in 

 harmful after effects on the crop. Its general influences, 

 besides its functions in the metabolic and synthetic 

 processes of plant development, may be listed briefly as 

 follows : 



1. Nitrogen tends to increase the growth of the above- 



ground parts. 



2. It delays maturity by encouraging vegetative growth. 



This oftentimes endangers the crop to frost, or 

 may cause trees to winter badly. 



3. It increases the ratio of straw to grain in cereals, and 



the ratio of leaves to underground parts in root 

 crops. 



