142 THE FIRST BOOK OF FARMING 



These properties may be grouped under three 

 heads : 



Physical properties ; the moisture, heat and air 

 conditions needed by the roots. 



Biological properties; the work of very minute 

 living organisms in the soil. 



Chemical properties; plant food in the soil. 



PHYSICAL PROPERTIES OF A FERTILE SOIL 



Three very important physical properties of a fer- 

 tile soil are its 



Power to take water falling on the surface. 



Power to absorb water from below. 



Power to hold water. 



The fertile soil must possess all three of these 

 powers. The relative degrees to which these three 

 powers or properties are possessed determine more 

 than anything else the kind of crops or the class of 

 crops that will grow best on a given soil. 



These powers depend, as we learned in Chapter 

 IV, on the texture of the soil or the relative amounts 

 of sand, silt, clay and humus contained in the soil. 



The power of admitting a free circulation of air 

 through its pores is also an important property of 

 a fertile soil, for air is necessary to the life and 

 growth of the roots. This property is dependent 

 also on texture. 



Two other important properties of a fertile soil 

 are power to absorb and power to hold heat. These 

 depend upon the power of the soil to take in warm 



