INFLUENCE OE SOLUBLE ORGANIC "MATTEK. 31 



EXEECISE XXII. 



■I'lIE INFLUENCE OF SOLUBLE OEGANIC MATTER ON NITRIFICA- 

 TION IN SOILS. 



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

 soil, in tumblers. 



2. Add 100 mgs. (NHJ^SO^ to each. 



3. Make further additions as follows : 



1 & 2 — nothing. 



3 & 4 — 1 gram dextrose. 



5 & 6 — 5 grams dextrose. 



4. Stir thoroughly by means of a sterile spatula. 



5. Inoculate all with 10 cc. (^ 5 gms. soil) of a 5-minute 

 infusion of a fresh sample of the soil. 



6. Add sterile water to bring the moisture conditions up 

 to the optimum for the soil. 



7. Cover with Petri dish covers, weigh, and record the 

 weight on the tumblers. 



8. Incubate 4 weeks at 20° C. 



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

 store that lost by evaporation. 



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

 about 2 gms. of lime; shake, filter, wash and determine the 

 nitrates present in aliquot portions of the leachings as usual. 



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