RELATION OF THE SOIL TO HEAT 43 



up in evaporating water. A sandy soil readily warms 

 up in the spring on account of the relatively small 

 amount of water which it contains. 



The specific heat of a soil is the amount of heat re- 

 quired to raise a given weight i° C, as compared with 

 the heat required to raise the same weight of water i°. 

 The specific heat of soils ranges from 0.2 to 0.4. 



The effect of drainage upon soil temperature is 

 marked. The surface of well-drained land is usually 

 several degrees warmer than that of poorly drained 

 land. Water being a poor conductor of heat it follows 

 that soils which are saturated are slow to warm up in 

 the spring. At a depth of 2 or 3 feet there is not such 

 a marked difference in the temperature of wet and dry 

 soils. It is to be observed that with proper systems of 

 drainage the surplus w T ater is removed from the sur- 

 face soil and stored up in the subsoil for the future use 

 of the crop, and at the same time the temperature of the 

 surface soil is raised, thus improving the conditions for 

 crop growth. The relation of drainage to the proper 

 supply of water and temperature for crop growth is a 

 matter which generally receives too little consideration 

 in field practice. 



40. Heat from Chemical Reactions within the 

 Soil. — Heat also results from the slow oxidation of 

 the organic matter of the soil. When organic matter 

 decomposes, it produces heat. A load of manure, when 

 it rots in the soil, gives off the same amount of heat as 



