RELATION OF THE SOIL TO HEAT 



39. The Sources of Heat in soils are (i) solar 

 heat, and (2) heat resulting from chemical action. 

 Solar heat is the main source for crop production. 

 The action of heat upon soils has been studied exten- 

 sively by Schiibler. The amount of heat a soil is 

 capable of absorbing depends upon its texture and 

 moisture content. All dark-colored soils have a 

 greater power for absorbing heat than light-colored 

 ones. From Schiibler's experiments it appears that 

 when dry, there may be as great a difference as 8 C., 

 between light- and dark-colored soils. When one set 

 of soils was covered with a thin white coat of mag- 

 nesia, and another set with lampblack, and exposed 

 under like conditions, the temperatures were : 6 



White coating. Black coating. 



Sand 43 50 



Gypsum 43 51 



Humus 42 49 



Clay 41 48 



L,oam 42 50 



The presence of water in the soil modifies the power 

 for absorbing heat. A sandy soil retains about 12 per 

 cent, of water, while a humus soil retains 35 per cent. 

 The additional amount of water in the humus soil 

 causes the soil temperature to be lower than that of 

 the sandy soil. While the humus soil absorbs more 

 heat than the sandy soil, the heat is used up in warm- 

 ing the water. A sandy soil readily warms up in the 

 spring on account of the relatively small amount of 

 water which it contains. 



