p'- 



.,^'',,0''' EXEECISE XX. 



37 



NITEIFICATION IN SOILS. 



■1. Weigh off in tumblers six 100 gram portions of an air- 

 dry, sieved sample of the soil to be tested. 



2. Arrange thus : i 4-^"^ 



1 & 2— nothing. 



3 & 4—100 mgs. (NI-l4)2S04. 



5 & 6—200 mgs. dried blood. 



3. Stir in these materials very thoroughly by means of a 

 sterile spatula. 



i. Add 10 CO. of a 5-minute infusion of a fresh sample 

 of the soil to each. 



5. Add sterile vs^ater to bring the moisture conditions up 

 to the optimum for the soil. 



6. Cover virith Petri dish covers. 



7. Weigh on a torsion balance and record the total weight 

 on the tumblers. 



8. Incubate for 4 weeks at 20° C. 



9. Weigh every ten days and by means of sterile water 

 restore that lost by evaporation. 



10. At the end of the incubation period add water and 

 about 2 gms. of lime, and shake thoroughly in a wide- 



' mouth bottle. 



11. Filter through folded filter paper and wash thor- 

 oughly. 



12. Make up to some convenient volume and determine 

 the nitrate present in aliquot portions, by the phenol-sul- 

 fonie acid method. 



