232 



MICROBIOLOGY OF SOIL. 



ganic matter and its ultimate mineralization proceed too fast. It often 

 happens that the farmer is unable to maintain a proper supply of humus 

 in these soils because of their openness and is forced to adopt measures 

 that will retard soil aeration. He resorts therefore, to rolling, marling, 

 manuring and green manuring. 



On the other hand, heavy, fine-grained soils are not sufficiently well 

 aerated to allow a rapid mineralization of the organic matter. Under 

 extreme conditions the decomposition processes do not keep pace with 

 the process making toward the accumulation of organic matter, and a 

 more or less considerable increase in the amount of the latter takes place. 

 This occurs in low lying meadows, and, more particularly, in bogs and 

 swamps. Hence the farmer attempts to intensify aeration and the 

 resulting mineralization of the humus by more thorough tillage, drainage, 

 liming and manuring. 



TEMPERATURE. 



INFLUENCE OF CLIMATE AND SEASON. An illustration of the differ- 

 ences that may exist in the soil temperatures of different regions is given 

 by a comparison of the mean temperatures of 1901 recorded at Moscow, 

 Idaho, and New Brunswick, New Jersey. The soil temperatures were 

 taken to a depth of 152 mm. (6 inches). 



Soil Temperature,* 1901. 



Air Temperatures* 1901. 



*Recorded in Fahrenheit scale. 



It will be observed that in the months of November to March the soil 

 temperatures in the two places were nearly the same. On the other hand, 

 in April to October the average temperatures at New Brunswick were 

 for soil 14.5 (58 F.) and for air 22.5 (72 F.), respectively; and in July 



