THE PRINCIPLES OF FERTILIZER PRACTICE 473 



encouragement of the natural fixation as well. Due to the 

 practical possibility of keeping up the nitrogen supply of the 

 soil by the proper use of farm manure, crop residues, green- 

 manures, and the utilization of legumes in the rotation, the 

 quantity of nitrogen purchased in commercial fertilizers 

 should be as small as possible if its use is to be profitable. 

 When so purchased it should function more or less as a crop 

 starter rather than as a source of any large amount of the 

 plants' supply of nutrient. 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 applica- 

 tion of soluble nitrogen, the average farmer is prone to ascribe 

 too much importance to its influence in proper crop develop- 

 ment. This attitude is unfortunate, since nitrogen is the 

 highest priced constituent of ordinary fertilizers and should 

 usually be purchased to a less extent than potash and espe- 

 cially than phosphoric acid. Moreover, of the three common 

 fertilizer elements, it is the only one which, added in excess, 

 will result in harmful after-effects on the crop. These pos- 

 sible and important detrimental effects of nitrogen may be 

 listed as follows : 



1. It may delay maturity by encouraging vegetative 

 growth. This oftentimes endangers the crop to frost, or may 

 cause trees to winter badly. 



2. It may weaken the straw and cause lodging in grain. 

 This is due to an extreme lengthening of the internodes, and 

 as the head fills the stem is no longer able to support the in- 

 creased weight. 



3. It may lower quality. This is especially noticeable in 

 certain grains and fruits, as barley and peaches. The ship- 

 ping qualities of fruits and vegetables are also impaired. 



4. It may decrease resistance to disease. This is probably 

 due to a change in the physiological resistance within the 



