62 FIELD AND LABORATORY STUDIES OF SOILS 



What influence does color have on the temperature of the 

 soil? When is this difference greatest? How would the 

 addition of organic matter affect the temperature of a soil? 

 Discussion : The color of soil is due to three things : 

 (1) The color may come from the original rock particles 



Fig. 25. — Corn Planted the Same Day. Dark surfaces absorb 



more heat than light objects. 



of which the soil is formed. An example of this is found 

 in white sandy soil from clear quartz sand. (2) The color 

 usually comes from material which sticks to the particles. 

 The coloring material may be either iron compounds or 

 organic matter or both. Red, yellow, blue, and gray 

 soils are colored by some form of iron, and any of these may 

 be darkened by the presence of organic matter. 



