RELATION OF THE SOIL TO HEAT 



39. The Sources of Heat in soils are (1) solar 

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

 Solar heat is the main source for crop produc- 

 tion. The action of heat upon soils has been 

 studied extensively 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 



Loam 42 50 



The presence of water in the soil modifies the power 

 for absorbing heat. A sandy soil for example retains 

 about 12 percent, of water, while a humus soil retains 

 35 per cent. The additional amount of water in the 

 humus soil may cause the soil temperature to be lower 

 than that of the sandy soil. While the humus soil 

 absorbs more heat than the sandv soil, the heat is used 



