NITROGEN FIXATION IN SOIL 



63 



2. Treat as follows 



(a) Control untreated 



(b) Add 2 per cent of manmt 



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 800-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 



No 



Treatment 



Nitrogen m loo gm of dry soil 



Total 



Average 



Gam due to 

 treatment 



I 



2 



3 

 4 



5 

 6 



Per cent 

 None 

 do. 

 do, 

 2 manmt 

 do. 

 do. 



Mgm 



Mgm 



Mgm 



