115- 



Table 



Given 100 sq. cm. of moist enrth 12 H deep 

 iCvapo ration per hour in grains 



Evaporation also depends on the lay of the land and varies with 

 the cover. For instance, 1 H mulch may "be reduced 1/3 or 4. It depends 

 on ho-* dry the soil is, and on the tillage. It varies also with the 

 character and also with depthshallow limestone soils "burn out". 



A living cover invariably reduces evaopr^tion from the soil it- 

 self altho the transpiration plus evaporation from the soil is greater. 

 The general average precipitation is about 30** 2JL this 50> evaporates, 

 runs off, yynd. Ifffe is, unaccounted for . 



Another source of loss of soil water is percolation, which is 

 the downward movement of water by gravity. The amount of loss in this 

 way is very gre- t; water percolates most rapidly in large spaces, and 

 whether these l^rge spaces are the result of coarse texture or of a 

 loose, cloddy structure, the final result is the loss of water. The rapi- 

 dity of such loss id directly dependent on the size and volume of the 

 pore spaces in the soil. 



jl. Temperature of soil. 



Soil temperature depends on watei*. sun and wind; on the color 

 of the soil, and other characteristics. The factors affecting soil tem- 

 perature may be mentioned as follows: 



1) Heat supply 



2) Specific gravity of the soil 



3) Specific he*t of the soil 



4) Color of the soil 



5) Attitude of the surface 



6 Conductivity of the soil 



7 Circulation of air above the so 1 



8 Water-content of the soil 



For further discussion of these factors read Lyon He Fippin, pa- 

 ges 4^3-463. 



Water is the, great regulator of soil temperature. In June, I8b9, 

 the following figures were obtained (Germany): 



Diurnal changes practically disappear about 3 feet down in the 

 soil. Yearly changes may be noticed as far down aa 75 feet. At 3 feet 

 down the temperature the temperature is about 2 F. 



