Chemical properties; plant food in the soil.
PHYSICAL PROPERTIES OF A FERTILE SOIL
Three very important physical properties of a fertile 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 rain and warm air, and also upon density and color. The denser or more compact soil and the darker soil having greater power to absorb heat.
The compactness of the soil which gives it greater powers to absorb heat weakens its powers to hold it, because the compactness allows more rapid conduction of heat to the surface, where it is lost by radiation.
The more moisture a soil holds, the weaker is its heat-holding power, because the heat is used in warming and evaporating water from the surface of the soil.