474 



STATE BOARD OF AGRICULTURE. 



Daily amount of ammonia produced by B. mycoides in the same sand with various moisture contents. 



(mg per 100 cc.) 



Coarse sand . . 

 Medium sand. 

 Fine sand. . . . 



Moisture. 



10% 



20% 

 10% 

 25% 

 15% 

 30^ 



0-2 

 days. 



2-4 

 days. 



63. 5 

 24-6 

 21.4 

 IS.S 

 7.7 

 15.6 



10.7 

 2.6 



56.7 

 9.2 

 3.9 

 6.0 



4-6 

 days. 



35.3 

 15.6 

 26.0 



6.1 

 SS.S 



5.9 



6-11 

 days. 



3.0 

 3.8 

 9.8 

 7.5 

 0.8 

 0.6 



11-21 

 days. 



3.7 

 0.5 

 2.1 

 0.4 

 1.0 

 0.9 



The second section of Table IX compares the daily ammonia for- 

 mation in each sand at the highest and lowest moisture content. The 

 maximum rate of decomposition in the coarse sand is within the first 

 two daj-s, regardless of the moisture content. In the medium sand, 

 the moisture content causes a difference; the drier soil has the maxi- 

 mum after two days, the moister soil before two days. In the finest 

 sand, the difference is still more pronounced, the moist sand having its 

 maximum in the first two days, while the drier sand does not show this 

 until after 4 days. 



The last section indicates Avhat percentage of the total ammonia 

 was formed in the various time intervals. The results agree with the 

 above conclusions. The averages show that the largest amount of am- 

 monia in the moist sands is formed in the first two davs, while in the 

 drier sands, it is formed at about the fifth day. 



The endiK)iut of decomposition will be influenced by drying if the 

 moisture film is interrupted and does no more allow a difiiusion from 

 one particle to the other. In this case, the distribution and number of 

 bacteria ])lay the deciding rule. A sand with 1 mm. grainsize contains 

 about 700 particles ]jcr gram; 0.1 nun. grainsize gives 700,000 particles, 

 and 0.01 mm. grainsize 700,000,000 particles per gram of soil. In fine 

 soils, only part of the soil particles will have bacteria, while others will 

 be sterile. If, in this case, the moisture film does not allow diffusion 

 from one particle to the other, the endpoint will depend upon the 

 number of cells in the soil. 



Influence of Ventilation. — It has been stated in several places that 

 the enormous increase of ammonia production in sand cultures is due 

 to the increased oxygen suj>i)ly which is regulated by the ventilation of 

 the soil. The ventilation, or permeability to air, of dry soil is propor- 

 tionate to the square of the grain diameter, according to King. Mathe- 

 matical relations between moisture content, grainsize and iwrnieability 

 are not known to the ^\''riter. It is safe to assume, however, that with 

 the same moisture content, the increase of grainsize increases the per- 



