CHAPTER IV 



RELATIONS OF SOIL TO HEAT 



Influence of Temperature on Life Sources of Soil Heat Influence of Latitude 

 and Aspect Temperature of Surface Soil Specific Heat of Soils Con- 

 ductivity of Soil Constituents Kadiation of Heat Influence of Water on 

 Soil Temperature Temperature of Subsoil Prevention of Summer Frost. 



Influence of Temperature on Life. All the processes of life, 

 whether in plants or animals, are only possible between 

 certain limits of temperature, below or above which life 

 cannot exist. Each kind of life has a range of temperature 

 more or less peculiar to itself, within which its functions may 

 possibly be performed ; it has also an optimum temperature 

 at which the greatest amount of vigour is exhibited ; this 

 optimum temperature may be different in different stages of 

 growth. All living beings have, however, some power of 

 adaptation to the circumstances in which they are placed. 



The life processes which occur in the soil are distinctly 

 affected by the temperature of the soil ; the germination of 

 seeds is one of the processes so affected. The seeds of some 

 plants, as rye, mustard, and lucerne, may undergo a very 

 slow germination at the freezing point, but for most seeds 

 a higher temperature is required. F. Haberlandt (Landw. 

 Ver sucks- Stationen, xvii. 104) experimented with a great 

 variety of seeds at four temperatures ; the lowest temperatures 

 at which germination took place were as follows : 



