METHODS 199 



Material Ammonified. The speed with which ammonia is formed 

 within a soil varies greatly, depending upon the nature of the 

 material to be ammonified. Lipman and his associates found the 

 following proportions of nitrogen were transformed into ammonia 

 in six days: 



Concentrated tankage 56.66 per cent. 



Ground fish 47.16 



Cow manure, solid and liquid excreta 32 . 60 



Dried blood 16.74 



Bone meal 16.65 



Cow manure, solid excreta 5.39 



Cotton-seed meal . . . . 4.95 



However, this order is not always maintained, for C. B. Lipman 

 has found it to vary with the soil and with the bacterial flora. 

 Lipman and Brown consider the carbon-nitrogen ratio important in 

 determining the rate of ammonification of nitrogenous materials, 

 and then the modification of this ratio by soluble carbohydrates or 

 by other soluble compounds may lead to changes in the numbers 

 and species of the microorganisms in the soil or culture solutions 

 and a consequent depressed or intensified ammonification, depend- 

 ing on the character of the nitrogenous fertilizer. 



The addition of dextrose, sucrose, lactose, maltose, and mannite, 

 according to Lipman and Brown, decrease the accumulation of 

 ammonia in the soil. Kelley found that by adding 1.586 gms. of 

 starch to 1.072 gms. of casein the quantity of ammonia in the soil 

 at the end of nine days was decreased 50 per cent. 



In the presence of the carbohydrates the decrease may be either 

 real or apparent. The true decrease may be due to the carbohydrate 

 which causes the organism to use only sufficient protein to meet its 

 nitrogen metabolism when only a small quantity of ammonia would 

 accumulate. 



The apparent decrease is probably due to an acceleration of the 

 speed with which ammonia is transformed into protein nitrogen. 

 Inert organic substances in general, such as starch, cellulose, and 

 peat, usually decrease the speed of ammonification. This is due, 

 according to Rahn, to the substance making some of the soil moisture 

 unavailable to the bacteria, for he found that when the moisture is 

 sufficiently great cellulose acts as a stimulant to ammonification, 

 probably by holding the sand particles farther apart and thus in- 

 creasing aeration. Dzierzbicki has found that small amounts of 

 some humic acid salts increase ammonification. 



The addition of manure to a soil greatly increases the ammonia 

 produced in a soil. This is illustrated by the following results 

 obtained by Greaves and Carter. In the first column is given the 

 per cent, of ammonia found, the untreated soil being taken as 100 

 per cent. The various quantities of manure were applied to the 



