UTILIZATION OF NITROGEN-FIXING POWERS OF LEGUMES. 109 



When these crops are thus plowed into the soil they are brought 

 at once within reach of the soil bacteria. 



The bacteria seize hold of the proteid products in the plants, as 

 well as the cellulose and other organic substances, and cause their 

 rapid decomposition. After this process is finished the nitrifying 

 bacteria in the soil oxidize the ammonia left after the decomposition 

 ceases and convert it into nitrate. Thus, after a few weeks, a con- 

 siderable portion of the nitrogen material which was fixed in the 

 legume has been converted into nitrate, available for plant life. 

 These remain in the soil and may be used by the next crop of plants 

 sown on the same field, thus increasing its yield by means of the 

 nitrogen which has been fixed by the legume and the bacteria 

 together, and has been converted into an available form by the soil 

 bacteria. 



A second method of utilizing the nitrogen is by converting it 

 into manure. The crop of legumes is reaped and fed to animals, 

 the roots and stubble only being plowed into the soil. The portion 

 fed to the animals is later returned to the soil as manure. Part 

 of the nitrogenous material is thus metabolized by the animal body 

 to urea, and part passes into the feces unassimilated, while part 

 remains in the roots and soil. But it is all eventually decomposed 

 by the putrefying bacteria, and goes through the same series of meta- 

 morphoses which we have already described in sufficient detail. The 

 result is that, in the end, most of it is returned to the soil in a form 

 available for plant life. This method of utilizing the nitrogen is 

 certainly the best economy, since it has a double advantage: The 

 nitrogen is used twice, once as a food for the stock and a second 

 time as a food for the crops in the form of manure. 



It is of course manifest that under either of these methods of 

 treatment not all of the nitrogen fixed by the legume and the 

 bacteria is rendered available for the next series of crops. At 

 the very best, part of it will be lost to the soil by the process of 

 putrefaction which liberates free ammonia, and by denitrification 

 which liberates free nitrogen. It is impossible, by any means now 

 at our disposal, to prevent this loss, and thus a portion of the fixed 

 nitrogen is, even with the best treatment, dissipated again into 



