NITROGEN FIXATION IN SOIL 



2. Treat as follows: 



(a) Control untreated. 



(b) Add 2 per cent, of mannit. 



3. Mix the mannit thoroughly with the soil by means of 

 a spatula. 



4. Raise the moisture content of the soil to optimum, 

 and at regular intervals of two days add water to replace 

 the loss by evaporation. 



5. Incubate these at 28 C. for from fourteen to twenty- 

 one days. 



6. Now prepare the soil for analysis. When dry, pass 

 it through a 20-mesh sieve, mix thoroughly, and draw a 

 small sample for analysis; about 100 to 150 grams is enough. 

 This smaller sample should be pounded in a mortar until 

 the entire mass passes through a loo-mesh sieve. Weigh 

 out from three to six portions of 10 grams each into 8oo-c.c. 

 Kjeldahl flasks. 



7. Analyze according to the Kjeldahl method (see p. 145). 



8. Run moisture determinations on the soil at the time 

 samples are taken for nitrogen analysis. 



9. Tabulate results. 



TABLE 26. Nitrogen Fixation in Soil 



