460 



THE PRINCIPLES OF SOIL MANAGEMENT 



it up most readily. The effect of the mulch is therefore 

 to maintain a more uniform soil temperature. The 

 presence of stone in the soil increases its temperature. 

 The movement of heat through the soil is also increased 

 decidedly by the presence of moisture. Pott found that 

 when a dry sand conducted 100 units of heat, the same 

 sand in a moist state conducted 174 units, and when 

 wet, 189 units, or nearly twice that for the dry sand. The 

 operation of rolling by compacting the soil increases 

 its conductivity for heat, and consequently its average 

 temperature. King found, as an average of several 

 trials on different soils, that at a depth of 1.5 inches, 

 rolled soil was 3.1 Fahr. warmer than the unrolled 

 soil, and at a depth of three inches the difference in 

 favor of rolling was 2.9 Fahr. In extreme cases, he 

 has found differences nearly three times as great as 



