48 SOILS AND FERTILIZERS 



than those light in color. Schiibler observed a differ- 

 ence in temperature of 8 C. between the same soils, 

 when given a white coating with magnesia and a black 

 coating with lampblack. 17 Black humus soils usually 

 contain so much water that the additional heat is utilized 

 for evaporation, and this results in the soil being cooler 

 than light-colored sandy soil. 



43. Specific Heat of Soils. Soils have a low specific 

 heat ; it requires only about one fifth as much to raise a 

 pound of soil i as is required to raise a pound of water 

 i. When soils are wet, the specific heat is greatly 

 increased, and they respond more slowly to the influ- 

 ence of the sun's rays. Sand has the lowest specific 

 heat of any soil constituent and retains the least water, 

 hence sandy soils warm up more readily than other soils. 

 On the other hand, clay soils, although slower to warm 

 up in the spring, retain their heat longer. 



44. Farm Manures and Soil Temperature. When the 

 animal and vegetable matter of the soil decays, heat is 

 produced. The slow oxidation of manure in the soil 

 yields in the end as much heat as if the dry manure 

 were burned. Whenever combustion or oxidation takes 

 place, heat results. 



Manured land is usually i or 2 warmer in the spring 

 than unmanured land. It has been estimated that the 

 amount of organic matter which undergoes oxidation in 

 an acre of rich prairie soil produces as much heat 



