34 LAND DRAINAGE 



The specific heat of loam to be .2154. 



The specific heat of peat to be .2525. 



The specific heat of water is 1.0000. 



Roughly, the dry sand, dry clay, and dry loam require 

 one-fifth as much heat to warm a given weight of them 

 through one degree as does water. The fact is more 

 impressive, usually, when conversely stated : it requires 

 five times as much heat to raise the temperature of a 

 pound of water one degree as to raise the temperature 

 of a pound of these soils one degree. 



52. Proper water content for agricultural soils. Hell- 

 riegel found that when soils experimented with contained 

 50 per cent to 60 per cent of the water they were capable 

 of holding, their moisture condition was best for producing 

 crops. If his findings are accepted, a soil may be said to 

 be in best moisture condition to support crops when it 

 contains a trifle over 50 per cent of the water it would be 

 holding if all of the space between its soil grains were full. 

 For sandy soils this will not be far from 15 per cent of their 

 own dry weight ; for loams, about 20 per cent ; for clays, 

 about 30 per cent ; and for the finer clays, perhaps as much 

 as 35 per cent. These amounts should be kept constant 

 during the germinating and growing periods of the crop. 



53. Effect of water on soil temperature. For loams, 

 the best quantity of water for crop production is near 20 

 per cent, or one-fifth of the dry weight of the soil. Thus 

 an amount of loam soil that would weigh 100 pounds 

 dry, should carry 20 pounds of capillary water, and with 

 this water would weigh 120 pounds. One hundred pounds 

 of water requires five times as much heat to raise its tem- 

 perature one degree as does 100 pounds of soil. Twenty 

 pounds of water requires just the same amount of heat to 

 raise its temperature one degree as does the 100 pounds 



