|Effect on soil
|The typical dark colour of many soils is caused by organic matter.
|May facilitate warming
|Organic matter can hold water up to 20 times its weight.
|Helps prevent drying and shrinking improves moisture retention in sandy soils.
|Combination with clay minerals
|Joins soils particles into structural units called aggregates.
Permits gas exchange;
Stabilizes structure; increases permeability.
|Forms stable complexes with Cu2+, Mn2+ Zn2+, and other polyvalent cations.
|Buffers the availability of micronutrients to higher plants
|Solubility in water
|Insolubility of organic matter results partially from its association with clay; salts of divalent and trivalent cations with organic matter are also insoluble; isolated organic matter are also insoluble; isolated organic matter is partly soluble in water.
|Organic matter buffers soil pH in the slightly acid, neutral, and alkaline ranges.
|Help maintain a unit form reaction (pH) in the soil
|Total acidities of isolated fractions of humus range from 3,000 – 14,000 mmol kg-1
|Organic matter brings about a 20-70% increase in CEC in many soils.
|Decomposition of Organic Matter Yields CO2, NH4 – PO43- and SO42-
|A source of nutrients for plant growth.
|Combination with organic molecules
|Affects bioactivity, persistence, and biodegradability of pesticides.
|Modifies the application rate of pesticides for effective control.
Source: Adapted From Stevenson (1982-18)