46 SOILS AND FERTILIZERS 



The manure enables the soil to retain more of the 

 moisture near the surface and prevents losses by perco- 

 lation. The difference in moisture content between 

 manured and unmanured land is particularly noticeable 

 in a dry season. 14 



Coarse leached manure may have just the opposite 

 effect by producing an open and porous condition of the 

 soil. 



RELATION OF SOIL TO HEAT 



39. Soil Temperature. The way in which a soil 

 responds to heat and cold is an important factor in its 

 crop-producing value. A soil temperature of 42 to 

 50 F. is required for crop growth, and the best condi- 

 tions do not exist until the soil has reached a tempera- 

 ture of 60 to 70 F. During cold springs in northern 

 latitudes the soil is often so cold as to retard the germi- 

 nation process, and to affect the vitality of seeds, caus- 

 ing a poor stand of grain. 



40. Heat required for Evaporation. It is estimated 

 that the heat required to evaporate a pound of water at 

 60 F. would raise the temperature of 1000 pounds of 

 water i F. When water evaporates, the soil is 



