150 STATE BOARD OF AGRICULTURE. 



complex bodies. This is the process of nitrification, or nitrate building. In most 

 species of plants the nitrogen necessary for their growth must be in the form of 

 nitrates in order to be dissolved and carried in the sap for ready assimilation by 

 the plant cells. The nitrifying organisms seize upon the ammonia which is formed 

 by the degradation of the complex nitrogenous bodies by the ammonifiers, and 

 by the addition of oxygen to it. they form nitric acid which combines readily with 

 chemical bases in the soil to form nitrates, thus placing the nitrogen at the dis- 

 posal of the plant. 



The nitrifying organisms differ from the preceding classes in their food re- 

 quirements in that, whereas the denitrifying and ammonifying organisms require 

 at least a trace of organic matter for their best development, the nitrifying 

 organisms do not require organic matter; in fact, they are incapable of growing 

 in the same, although its presence in the soil to a certain extent does not prove 

 fatal to their existence. Hence the advisability of putting too much manure on 

 the land is to be doubted, inasmuch as there would be danger that the reducing 

 bacteria, together with the leaching, would cause the loss of considerable nitrogen 

 before a condition was arrived at under which the nitrifying organisms would be 

 able to thrive. 



Another point which is just as essential to the rapid development of the 

 nitrifying organisms as a proper food supply, is that they should be furnished 

 an abundance of oxygen, as they fail to perform their functions in its absence. 

 Here is further shown the necessity for thorough cultivation in order to afford 

 this supply. This fact would also suggest caution against too frequent fallowing 

 of the land. If it is plowed, rolled down, and allowed to lie in that condition, 

 nitrification would be diminished by lack of aeration and the reduction in moisture 

 content. On the other hand, experience has shown that fallowing with frequent 

 and thorough cultivation often gives beneficial results, due possibly to increased 

 nitrification, with the result that, in the absence of a crop, the nitrates thus 

 formed would be conserved. 



NITROGEN-GATHERING BACTERIA. 



When seeds of plants not belonging to the clover family are placed in soil 

 entirely destitute of nitrogen, but containin.g all the other chemical elements 

 necessary for plant growth, they "vMll start to grow, but as soon as the food 

 material stored up in the seed itself is exhausted, the plants will wither and die. 

 On the other hand, if seeds of the legumes be placed in the same soil, they will 

 also make a start. Then they begin to wither, and undergo a period of "nitro.gen 

 hunger," after which they revive and make a vigorous growth. It is only in com- 

 paratively recent years that this phenomenon has been understood. If examina- 

 tion is made of the roots of peas, beans, clovers, alfalfa, and other plants belong- 

 ing to the same family, there will be found on the roots, small tubercles or 

 nodules. "When cut open and examined under the microscope, these are found 

 to contain myriads of bacteria which, by experimental investigation, have been 

 proven to possess the property of extracting free nitrogen from the air. Thus it 

 is that the clovers, themselves so rich in nitrogen, enrich the soil by bringing to 

 it so much more nitrogen than they use up. 



This phenomenon of extraction of nitrogen from the atmosphere is often suc- 

 cessfully made use of in a practical way in reclaiming fields deficient in nitrogen. 

 Fields that are badly run down through successive cropping, may be a.gain made 

 to yield by inoculating with soil from a field which has recently borne a good 

 crop of some legume, and sowing a leguminous crop. A good stand may often be 

 secured in this v.-ay when other methods fail. 



"Whether organisms from one legume will produce nodules on other legumes 

 and extract nitro.een from the air is still somewhat of an open question. At first 

 it was thought that each species of legume would grow only one species of 

 nitrogen gathering organisms. However, the results of recent research indicate 

 that the nodular organisms from any host may produce nodules on any other host, 

 but that they undergo more or less morphologic change in the transfer. 



It is supposed that the nitrogen-gathering organisms utilize the free nitrogen 

 of the air only in proportion to the poverty of the soil in available nitrogen. In 

 other words, the plant does not extract the free nitrogen from the air to any 

 extent unless it is forced to do so. Hence it would be unnecessary to use a fertil- 

 izer containing nitrates on a field intended for a leguminous crop. 



