AVAtLABILITY OF NITEOGENOtJS OEGANIC MATTER. 19 



EXEECISB XIII. 



THE AVAILABILITY OF NITROGENOUS OEGANIC MATTER AS IN- 

 DICATED BY ITS AMMONIFICATION. 



1. Weigh of? twelve 100 gram portions of air-dry, sieved 

 soil, in tumblers. 



2. Make additions of organic nitrogen, using amounts 

 equivalent to 155 milligrams of nitrogen, as follows: 



3. 



1 & 2 — concentrated tankage. 

 3 & 4— dried blood. 

 5 & 6 — cottonseed meal. 

 7 & 8 — bone meal. 



9 & 10 — horse manure (dried and ground). 

 11 & 12 — cow manure (dried and ground). 



4. Stir in these materials thoroughly by means of a sterile 

 spatula. 



5. Add sterile water to bring the moisture content of 

 the soil up to the optimum, making further additions in 

 each ease to provide organic matter containing 70% of 

 water. 



6. Cover with Petri dish covers and incubate for 7-8 days 

 at 20° C. 



7. Transfer to copper flasks, distil and determine the am- 

 monia formed, in the usual way. 



