Agriculture Reference
In-Depth Information
improved research equipment and practices are showing that soil organic
matter is even more vital than its early advocates recognized.
Soil organic matter is made up of plant and animal remains that have
been partially disintegrated and decomposed, as well as organic compounds
that have been synthesized by soil microorganisms. About 60 to 80 percent
of soil organic matter consists of humus (humic material), a complex mixture
of organic compounds formed by microbial activities. Humus, which is quite
resistant to further decomposition, is made up of fulvic acid, humic acid, and
humin. Fulvic acid is the most susceptible to decay by microbes and breaks
down over 15 to 50 years. Humic acid is more stable, lasting at least 100
years. Humin is the most stable and highly resistant to degradation.
Soil organic matter is important to organic fruit growers for a variety of
reasons:
Improves CEC and nutrient uptake.
Humus, one of the components of soil
organic matter, increases the soil's cation exchange capacity (CEC), which
refers to the soil's ability to bind and hold positively charged plant nutrients.
Humus has a much greater cation exchange capacity than the mineral por-
tions of the soil. As humus concentrations increase, so does the soil's ability
to store positively charged plant nutrients. Further, humus enhances mineral
breakdown, making nutrients more available to plants as organometal com-
plexes (specialized organic compounds that include metallic elements) that
form with ions, such as Fe , Cu , Zn , and Mn . These organometal com-
3+
2+
2+
2+
plexes are more available for plant uptake and use than the mineral form of
the elements.
Increases soil aggregates.
Soil organic matter is also critical in binding
mineral soil particles into stable aggregates. These aggregates combine to
form the macro- and micropores in the soil that are critical for water infilt-
ration and drainage. The presence of aggregate-building organic matter im-
proves the drainage of fine-textured soils, yet also improves the water-hold-
ing capacity of sandy soils. Aggregated soils are less susceptible to erosion
