v.] 



HEAT REQUIRED TO WARM SOIL 



129 



when compared with that of water ; hence soils which 

 retain much water will require far more heat to raise 

 their temperature than dry soils would. In consequence, 

 clay and humus soils are cold because the water they 

 retain gives them a high specific heat, they require more 

 of the sun's rays in spring to bring them up to the 

 proper temperature for growth, while sandy and other 

 open-textured soils are warm because of their dryness. 



If the figures given by Oemler for the specific heats 

 of various soils be combined with their approximate 

 densities and with their minimum capacity for water, the 

 following results are obtained for the specific heats of 

 certain typical soils in a saturated but completely drained 

 condition — 



The sandy soil only requires about half as much 

 heat to raise its temperature by a given amount as 

 would be needed by the peaty or clay soil, when all the 

 soils are in a wet but thoroughly drained condition ; of 

 course if the clay or peat were inadequately drained, so 

 that a higher proportion of water was retained, their 

 specific heats would approximate still nearer to that 

 of water. 



Just as a clay soil is slow to warm in the spring, its 

 high specific heat causes it to cool correspondingly 



