514 EXPEEIMENT STATION EECOED. 



In continuation of studies of ammonifieation and nitrification of green manures, 

 14 species of bacteria were identified as apparently closely connected with tlie 

 decomposition of buried Sann hemp, and their physiological and morphological 

 characters were studied. No one species of bacteria capable of attacking 

 cellulose was found, although this result was produced by two or more associated 

 bacteria. 



The investigations indicated that soil fungi play an important part in break- 

 ing down cellular tissue. The fertilizing value of green manures appears to 

 depend upon the rapid formation of simple nitrogen compounds, such as 

 ammonia, from proteid substances. It was found that the nitrification of 

 ammonia " is interfered with by the fact of its concentration and also by the 

 presence of soluble organic substances, some of which, at least, are strongly 

 toxic to nitrifying bacteria and in less measure to others; this condition 

 persists so long as the water extract remains acid to litmus, which under ordi- 

 nary conditions of manufacture might extend to as much as six weeks. . . . 

 The rapid ammonifieation which takes place when green manure is placed in 

 water and allowed to ferment was found to be accompanied by the develop- 

 ment of large numbers of ciliates, flagellates, and amoebae, whose presence 

 does not appear in this instance to be prejudicial to the activity of ammoni- 

 fying bacteria." It was also found " that ammonifieation is the necessary 

 antecedent to nitrification in the case of organic matter, that this process is 

 furthered by a high percentage of moisture, that high concentrations of am- 

 monia inhibit nitrification, but that such ammonia is absorbed by the soil and 

 can then be nitrified." 



The most complete and rapid nitrification was secured "by producing 

 anaerobic conditions with water saturation and subsequently draining and 

 aerating; the rapidity with which nitrification takes place under these condi- 

 tions depends upon the relative completeness of the anaerobic and subsequently 

 of the aerobic conditions." Under anaerobic conditions produced by water 

 saturation " toxins were produced which not only inhibited nitrification before 

 the ammonia concentration was sufficient to do so but afforded water extracts 

 which were toxic to seedlings and to bacteria; subsequent aeration removes 

 this toxic condition and the formation of nitrates takes place, the ultimate 

 result being a high percentage of nitrification of the nitrogen of the organic 

 matter. ... In connection with the nitrification of green manure it was 

 found that a loss of nitrate invariably occurred between the eighth and 

 twelfth weeks of the process in the laboratory," but the cause of this was not 

 determined. 



Mustard oil cake furnishing nitrogen equivalent to 1 per cent of the dry 

 weight of soil was added to a soil rich in lime without interfering with the 

 normal rate of nitrification. Although the rate of nitrification was in direct 

 proportion to the lime content, it was found that a soil low in lime in time 

 attained the same nitrate concentration as one high in lime. 



Azotobacter isolated from various soils showed marked differences in mor- 

 phological and cultural characters and in nitrogen-fixing capacity. Nitrogen 

 fixation by a pure culture of Azotobacter isolated from Pusa soil " was in- 

 creased by the additions of basic slag or humus to the ordinary medium, but 

 was diminished by the substitution of magnesium carbonate for calcium car- 

 bonate. . . . The addition of a seer [2.0.57 lbs.] of cane sugar to a plat 2 sq. 

 yds. in area resulted in an increase, in the nitrogen content of the first 6 in. of 

 soil, of nearly 15 per cent in 10 weeks. . . . 



" It was found possible to measure the relative toxicity of various bacterial 

 species to an intermediate form (Bacillus prodigiosus) and to one another 

 by use of plate cultures and the measurement of the rate of CO2 formation in 



