NITEOGJiN rCXATXON IN SOILS. 45 



BXEECISB XXXIV. 



NITKOGEN FIXATION IN" SOILS. 



1. Weigh off six 100 gram portions of air-dry, sieved soil, 

 in tumblers. 



2. Add 1 gram of mannite to each. 



3. Stir in thoroughly by means of a sterile spatula. 



4. Arrange thus: 



1 & 2— Infusion Soil 1. 

 3 & 4^Infusion Soil 2. 

 5 & 6 — Infusion Soil 3. 



5. Inoculate in duplicate with 10 cc. (= 5 gms. soil) 5- 

 minute infusions of three soils of different types. 



6. Add sterile water to bring the moisture conditions up 

 to the optimum for the soil. 



7. Cover with Petri dish cover and incubate 10-14 days 

 at 20° C. 



8. Eemove, dry, grind and analyze for total nitrogen by 

 the regular Kjeldahl method. 



9. Grind a sample of the air-dry soil used as the medium 

 and determine the total nitrogen present. 



10. The difference between the total nitrogen in the be- 

 ginning and at the end of the experiment gives the amount 

 of nitrogen fixed in the soil, and the relative fixing powers 

 of the different soils may thus be determined. 



