Agriculture Reference
In-Depth Information
Water layer aerobic
Microaerobic
zone
A
naerobic
zone
Ped
Figure 4.5.
Aerobic, microaerobic, and anaerobic zones in a soil ped.
may include, in low concentrations, oxides, particularly those of silicon, alu-
minum, iron, and titanium. These compounds move down the soil profile some-
times contributing to formations such as the spodic horizon, which can contain
aluminum and iron oxides along with highly decomposed carbon.
A large variety of dissolved organic compounds are released by decomposi-
tion of organic matter or from the activities of plants and animals in soil. These
compounds range from relatively simple molecules such as acetic acid, to rela-
tively complex materials such as enzymes and antibiotics and various cellular
components released on cell lyses (see Chapter 3). These and intermediate
products serve as sources of carbon and energy for organisms in soil and thus
do no persist. However, it is possible for almost any relatively simple water-
soluble organic compound to be found in the soil solution at any given time.
Other inorganic and organic compounds are brought into solution by the
decomposition of their parent materials. Rocks and minerals will be decom-
posed by physical, biological, and chemical mechanisms. Enzymes released
into the soil solution by microorganisms will decompose insoluble organic
materials such as wood. Most of the organic material released with be taken
up by the organism releasing the enzyme, but some will find its way into the
soil solution.
4.7.
INORGANIC IONS IN SOLUTION
Ionic species are generally more soluble in water than are neutral molecules.
The polar hydrogens in water are associated with anions and the partially
