THE LOSS OF NITROGEN. 91 



in the air. It is quite necessary for the continuance of soil fertility 

 that this lost material should be restored. 



Our farm lands slowly become incapable of supporting the 

 crops demanded of them. This loss of fertility in worn-out farms 

 is due, doubtless, to a number of factors, but the loss of nitrogen 

 is certainly the most prominent one. All over the agricultural 

 world it has been found necessary to replace this lost nitrogen in 

 the soil. For this purpose we have depended mostly upon commer- 

 cial fertilizers, which commonly contain nitrogen in the form of 

 nitrates. Of such fertilizers there is . a small supply in the 

 world, chiefly in South America, and as they are brought from 

 long distances they are sold at high prices. But the few large 

 deposits of nitrates in the world are being rapidly exhausted. 

 The high prices of nitrates are necessary and are bound to increase 

 as the soil needs them more and more and as the supply diminishes. 

 Clearly enough, the supplying of the lost nitrogen will become 

 more and more expensive as the great nitrogen stores are used up. 

 The seriousness of this problem of a constant draining of nitrogen 

 from the soil has been quite prominent in the minds of chemists 

 and agriculturists, as they have learned in the last few years the 

 significance of nitrogen for agriculture. 



The continuation of agriculture depends upon the existence 

 of some means of reclaiming the nitrogen from the atmosphere 

 for the use of plants. If there is no such means it is evident that 

 the nitrogen store of the soil will be used up and vegetation will 

 eventually, and, in highly cultivated lands, speedily die of nitrogen 

 'starvation. If, on the other hand, there is a possibility of reclaiming 

 such lost nitrogen there is no need of nitrogen starvation, since there 

 is an absolutely unlimited store of this, element in the form of the free 

 nitrogen of the air. It is quite evident that there is some means 

 within the reach of organic nature for making us6 of this atmos- 

 pheric nitrogen. Vegetation has continued on the earth for an 

 unknown number of centuries without any apparent diminution of 

 the nitrogen supply. This would not have been possible unless 

 the soil could have obtained from the air a stock of nitrogen to 

 replace that lost by the processes already indicated. 



