RECLAIMING LOST NITROGEN. 157 



bacteria together, and converted into an available form by the 

 soil bacteria. 



A second method of utilizing the nitrogen is by reaping 

 the crop of legumes and feeding it to animals, subsequently 

 returning the manure to the soil. The phenomenon that 

 occurs here is essentially that already noticed. Part of 

 the nitrogenous material is metabolized by the animal body 

 to urea, and part passes into the feces unassimilated. But 

 whether reduced to urea or not, it is eventually decomposed by 

 the putrefying bacteria, and goes through the same series of 

 metamorphoses which we have already described in sufficient 

 detail. The result is, that in the end, a portion of it is returned 

 to the soil with the manure in a form available for plant life. 



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 more particu- 

 larly by the denitrification which liberates a certain quantity of 

 free nitrogen. It is impossible, by any means now at our dis- 

 posal, to prevent this loss, and thus a portion of the fixed 

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

 the air. But by proper treatment this loss can be reduced to 

 a minimum and there may always be a surplus of gain. Even 

 taking into account all the nitrogen loss that comes from these 

 processes the use of a leguminous crop, upon a soil poor in 

 nitrogen, furnishes to that soil for the next crop a store of 

 nitrogen considerably in excess of that which it possessed 

 before. 



It is clear that here is a means at the disposal of agriculture 

 for replacing nitrogen. By the proper alternation of legumi- 

 nous plants and those which cannot fix nitrogen but simply 

 use it, it would seem to be theoretically possible to keep the 

 fertility of the soil, so far as concerns nitrogen, in a constant 



