MICROORGANISMS AS A FACTOR IN SOIL FERTILITY. 



2 33 



they were 20.0 (68 F.) and 24.5 (76.4 F.) respectively. It will also 

 be observed that there is an unmistakable relation between the corre- 

 sponding air and soil temperatures. 



As a further illustration of the relation of climate to temperature a 

 comparison may be made of the average daily mean temperatures at 

 Bismarck, North Dakota, for the period 18731895, and at Key West, 

 Florida, for the period 1872-1895. ^ j 



Daily Mean Temperatures* (Air). 



*Recorded in Fahrenheit scale. 



It is obvious from the figures given here that, because of the important 

 temperature variations of different soil regions, the microbiological activi- 

 ties must be profoundly modified. But apart from the climatic variations 

 already indicated there are seasonal variations in any particular locality 

 that are of great moment for soil microbiological activities. Such differ- 

 ences are demonstrated by the temperatures of 1898 and 1902, taken to a 

 depth of 152 mm. (6 inches), at New Brunswick, N. J. 



Soil Temperatures.* 



*Recorded in Fahrenheit scale. 



In this instance, the season of 1898 was not only earlier, but the tem- 

 peratures of June to September were sufficiently higher to favor more 

 intense bacterial growth and activity. 



EARLY AND LATE SOILS. Under any given climatic conditions the 

 warming up of soils in the spring will depend on their chemical and 

 mechanical composition, color, tillage and topography. Because of the 



