PropertyRemarksEffect on soil
ColourThe typical dark colour of many soils is caused by organic matter.May facilitate warming
Water retentionOrganic matter can hold water up to 20 times its weight.Helps prevent drying and shrinking improves moisture retention in sandy soils.
Combination with clay mineralsJoins soils particles into structural units called aggregates.

Permits gas exchange;

Stabilizes structure; increases permeability.

ChelationForms stable complexes with Cu2+, Mn2+ Zn2+, and other polyvalent cations.Buffers the availability of micronutrients to higher plants
Solubility in waterInsolubility 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. 
pH relationsOrganic matter buffers soil pH in the slightly acid, neutral, and alkaline ranges.Help maintain a unit form reaction (pH) in the soil
Cation exchangeTotal acidities of isolated fractions of humus range from 3,000 – 14,000 mmol kg-1Organic matter brings about a 20-70% increase in CEC in many soils.
MineralizationDecomposition of Organic Matter Yields  CO2, NH4 – PO43- and SO42-A source of nutrients for plant growth.
Combination with organic moleculesAffects bioactivity, persistence, and biodegradability of pesticides.Modifies the application rate of pesticides for effective control.

Source: Adapted From Stevenson (1982-18)

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