NITROGEN FROM THE AIR. 117 



Boussingaiilt, iu his experiments upon his farm, found that 

 the best devised practical rotation, aiming at an economy of 

 nitrogen phmt-food, would annually require, iu a five years' 

 course, not less than forty pounds of nitrogen per acre. He 

 raised potatoes, wheat, clover, turnips, and oats. In fact, 

 there would be no reasonable cause for a difference of 

 opinion regardiug the degree of importance we have to assign 

 to the air as a source of nitrogen plant-food, were it not for 

 the fact that, plants and soil are known to absorb at all times 

 more or less of it from the air, without the assistance of rain- 

 fall, etc. 



The value which ought to be conceded to this almost unin- 

 terrupted reaction of the plant and the soil on the available 

 nitrogen compounds of the air, has been variously estimated 

 by different investigators, and subsequently furnished the ma- 

 terial for dissentiug views regarding the propriety and the 

 economy of an additional supply of nitrogen plant-food to 

 our crops. The extreme views at first entertained on both 

 sides concerning the particular importance of nitrogen, for the 

 production of good crops, have since been compromised. 



Years of careful experimental inquiry under well defined 

 circumstances have made us better acquainted with the rela- 

 tive importance and the jnutiial dependence of the various ar- 

 ticles of plant-food on each other for the production of an 

 increased vc2:etal)le o-rowth. 



The nitrogen is now recognized as in a peculiar degree im- 

 portant for a luxuriant development of the cellular system ; 

 yet also considered powerless, like potassa or phosphoric 

 acid, without an adequate supply of the essential ash constit- 

 uents of the plants under cultivation. 



To-day there is practically but one opinion regardiu"* the 

 importance of the air as a source of nitrogen plant-food. 

 Since Boussingault, Sachs, Ville, Gilbert and others have 

 experimentally confirmed, by raising plants in an artificial at- 

 mosphere of ammonia, that all broad-leafed plants in particu- 

 lar absorb at all times more or less nitrogen plant-food from 

 the surrounding air, a greater importance is generally con- 

 ceded to the latter as a valuable resource in the case of lejru- 

 minous plants, as clover, and of a perennial growth like for- 

 ests and meadows. 



