SOIL HEAT 



233 



ture. Organic matter will lighten and loosen a soil, and lower 

 the volume weight. Moreover, its heat capacity is low. The 

 effect of such an addition is to lower the specific heat figure. 

 It is apparent also that the finer the texture of the soil, the 

 lower the specific heat. That is due not to a difference in 

 chemical composition but to a lowered volume weight. Any 

 practice, therefore, that tends to vary volume weight will in 

 a like manner vary specific heat. The farmer may encourage 

 the warming of his soil by deep and efficient plowing. By 

 increasing its organic content, he may create a tendency in 

 the same direction. 



One other factor, more important than those already men- 

 tioned, yet remains to be discussed. This is water, so univer- 

 sally present in soils and so important in natural soil phe- 

 nomena. As the specific heat of water is several times greater 

 than that of the soil constituents, any addition of it must raise 

 the thermal capacity of the mass. The following data from 

 IJlrich 1 show that moisture rather than texture and organic 

 matter is the controlling factor in normal soil: 



Table XL VIII 



THE EFFECT OF MOISTURE ON VOLUME SPECIFIC HEAT OF SOIL 

 (moisture expressed as a percentage of the total water capacity) 



The overwhelming influence of moisture is at once evident 

 from these data. Fine texture, because of its high water 

 capacity, usually accentuates the dominance of moisture. 

 Organic matter functions in the same way. While an organic 



1 Ulrieh, E., Untersuchungen uber die W armekapazitat der BodenTconsti- 

 tuenten; Forsch. a. d. Gebiete d. Agr.-Phys., Band 17, Seite 27, 1894. 



