780 PRINCIPLES OF SOIL MICROBIOLOGY 



increase, the curves agreeing closely with the temperature curve. Un- 

 der favorable temperature conditions, rainfall becomes the limiting- 

 factor as well as the oxygen brought down by the rain. In general 

 they have observed a period of spring activity, summer sluggishness, 

 autumn activity, followed by winter inertness. Woitkiewicz 39 also 

 found bacterial numbers to be highest in spring and lowest in winter; 

 the ratios of nitrogen-fixation in solution, in the seasons of winter, 



Dry 15 Percent 30Pcrcertf 45 Percent SOPercent- 75PcV«"t • 



■ Mi llijroros ot rtmmomo in Soil » P«pton«. __. __ dilhqrcirn ol A-VKtma in Soil *• B!o»d Meat. 



— — — . Milligrorns of Ammonia in Soil 'Lime — Milligrams of Ammyn\a in Normal Soil 



— . Bacteria in millions per lOq/ams ot soil containing Peptone. 



.. — -.„ Bacteria 111 million* per \0 qreme ot »oit contoinmg Blood Meal 



Fig. 74. Influence of moisture content of an Oregon soil upon ammonia for- 

 mation and bacterial development from peptone and blood meal, 75 per cent 

 moisture being that of full saturation (from Beckwith, Vass and Robinson). 



spring, summer, and fall were as l:2:2f:3. This may be due to the 

 greater abundance of available energy in the fall of the year. Deni- 

 trification was highest in fall and lowest in spring. By the use of the 

 Remy method, it was 40 found that the urea-decomposing, nitrifying, and 



39 Woitkiewicz, A. Beitrage zur bakteriologischen Bodenuntersuchungen. 

 Centrbl. Bakt. II, 42: 254-261. 1914. 



40 Lohnis, F., and Sabaschnikoff, A. t)ber die Zersetzung von Kalkstickstoff 

 und Stickstoffkalk. Centrbl. Bakt. II, 20: 322-332. 1908. 



