IDEAL FERTILIZERS 67 



soil impoverished to the extent of these operations. 

 Some people, knowing their soil is too wet to permit ni- 

 trification, apply nitrate of soda. Such application is 

 of benefit, for the plants get part of the nitrates, but there 

 is such a substantial loss through denitrification the 

 grower will find it far more profitable to secure good 

 drainage and keep his land in proper condition. Denitri- 

 fication takes place also when a large amount of green 

 vegetation is plowed under. By such course, fertility is 

 lost instead of gained. 



Fixation of Atmospheric Nitrogen Another class of 

 friendly organisms are the nitrogen-fixing bacteria. The 

 ammonifying and nitrifying bacteria, though most valu- 

 able in changing nitrogen to available form, do not in- 

 crease the soil content of nitrogen. These little friends, 

 the nitrogen-fixing bacteria, take free nitrogen from the 

 air and convert it into nitrogen compounds that can be 

 used as plant food. There are two classes of nitrogen- 

 fixing bacteria: "(1) Those bacteria that live in the soil 

 itself, independent of the presence of growing plants, and 

 (2) bacteria that are dependent upon the presence of 

 certain higher plants, living and working within the 

 plant roots." Those of the first class which are known 

 as "non-symbiotic" are seemingly of no great importance, 

 adding little to the store of combined nitrogen. 



Those in the second class are called "symbiotic." The 

 word symbiotic means "living together," but it is custom- 

 ary to use this word only when the association is of 

 mutual advantage. In this instance the bacteria give 



