Agriculture Reference
In-Depth Information
Figure
9.6.
Rock collected from badly eroded fields on a hillside in the Philippines used
to construct “dams” or bunds to prevent water eroding the soil. Ocean is visible in the
background.
9.5
SOIL COMPLEXITY
Soil is complex in that it is made up of air, water, and solids. Making it even more
complex is that soil air is different from atmospheric air, soil water is a solution of
inorganic and organic ions and molecules, and the solid portion is made up of both
inorganic and organic components. The inorganic components have different sizes,
composition, and activities in soil. The organic components represent all compounds
of biological origin in addition to humus synthesized during the decomposition of
organic matter. It is organic but is nothing like the compounds from which it is made.
In addition soil components do not act independently of each other. Inorganic com-
ponents, sand, silt, and clay along with organic matter combine into what could be
called a secondary structure. These secondary structures, called peds, lead to a soil
having improved crop-growing capabilities. In addition air and water are trapped in
pores in soil and thus are an intricate part of this secondary structure.
In addition to these complexities, soils in the field are different depending on how
they are formed and from what they are formed. If rock is pulverized, it forms a powder
that can be any color but is commonly gray and thus is very different from soil. In the
