60 



Elementary Principles of Agriculture 



Fig. 35. Temperature 

 curves of dry and wet 

 soils. 



The amount of water in the soil affects the tem- 

 perature more than the kind of soil. Much heat is re- 

 quired to warm and dry out wet 

 soils. Most of the heat is consumed 

 in evaporating the water. The 

 evaporation of water from the soil 

 may be compared to the evapo- 

 ration of sweat from the body, 

 because it cools the soil, just as 

 evaporation cools the body 



The texture of the soil also 

 affects the temperature. Coarse 

 rocky or lumpy soils suffer from 

 sudden changes in temperature. 

 Loose and well- cultivated soils 

 absorb and retain the sun's heat 

 best; and the temperature in such soils is more uniform. 

 The color of the soil affects the amount of heat 

 absorbed from the sun's rays. Dark-colored bodies 

 absorb the heat rays more readily than light ones. This 

 explains why dark soils are warmer than light soils. 



While a compact soil will absorb heat more rapidly 

 from the sun's rays than a loose one, it will also lose heat 

 more quickly, because of the more rapid conduction 

 of the heat to the surface, where it is lost by radiation. 

 Moist soils warm up more slowly than dry ones, be- 

 cause the heat is used up in warming and evaporating 

 the water. (Fig. 35.) 



94a. Absorption of Heat] from the Sun by Dry Soils. Air-dry 

 soils should be put into uniform vessels Gardeners' flats are 

 quite suitable. Insert ordinary dairy thermometers into the soil for 

 about two inches and note the temperature in each box. Put the 

 box in strong sunlight and make readings at 8, 10, 12, 2. 4, and 

 6 o'clock. Record the temperature as shown in Fig. 35. 



