FIXATION OF NITROGEN 



131 



sow a small <|uan1itv of the seed in question with the regu- 

 lar crops. Tims, if it is desired 1o secure a catch of alfalfa 

 on soil that has not grown this crop, instead of inoculation 

 with a pure culture or infected soil, some farmers follow 



ORGANIC) MATTER 



ANIMALS PLANTS 



{8g93fi 



SOLID LIQUID BODY BODY 



PUTREFACTION AND DECAY 



APflONiriCATION AMMONIA NM. A6SO8tO BY PIAMT 



* 



Fig. 28. The Cycle of Nitrogen 



After Wright. 



the practice of sowing a small quantity of alfalfa seed with 

 all of their grain crops, even if the land is seeded down to 

 red clover. In a few years this preliminary inoculation suf- 

 fices to infect the soil sufficiently so that inoculation of the 

 crop can be readily secured later. 



The matter of inoculation is especially important when a 

 new legume is to be grown or when a legume is to be sown 

 on a field on which it has not been grown for a number of 

 years. The bacteria are able to grow in the soil itself. 

 Kxperience has shown that they gradually decrease in num- 

 ber, and after five or six years will be so diminished that 

 inoculation is advisable if the legume is to be grown again. 



It has been shown that the composition of the plant is 

 changed by the presence of the nodules in that the nitro- 



