SOIL TEMPERATURE 



59 



steams in cold weather. You doubtless know that 

 manure from the horse stable is often used to furn- 

 ish heat for hotbeds and for sweet potato beds. 



Now the heat which warms the manure and sends 

 the steam out of it, and warms the hotbed and sweet 

 potato bed, is produced by the decaying or rotting 

 of the manure. More or less heat is produced by 

 the decay of all kinds of organic matter. So if 

 the soil is well supplied with organic matter, the 

 decay of this material will add somewhat to the 

 warmth of the soil. 



HOW SOILS LOSE HEAT 



Wet one of your fingers and hold your hand up 

 in the air. The wet finger will feel colder than the 

 others and will gradually become dry. This is be- 

 cause some of the heat of your finger is being used 

 to dry up the water or change it into a vapor, or in 

 other words to evaporate it. 



In the same manner a wet soil loses heat by the 

 evaporation of water from its surface. 



Experiment. Heat an iron rod, take it from the 

 fire and hold it near your face or hand. You will 

 feel the heat without touching the rod. The heat 

 is radiated from the rod through the air to your 

 body and the rod gradually cools. In the same way 

 the soil may lose its heat by radiating it into the 

 air. A clay soil will lose more heat by radiation 

 than a sandy soil because the clay is more compact. 



