Components of Soil Organic Matter
Most soil organic matter originates from plant tissue. Plant residues contain 60-90 percent moisture. The remaining dry matter consists of carbon (C), oxygen, hydrogen (H), and small amounts of sulphur (S), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg).
Although present in small amounts, these nutrients are very important from the viewpoint of soil fertility management.
Soil organic matter consists of a variety of components. These include, in varying proportions and many intermediate stages, an active organic fraction including microorganisms (10-40 percent), and resistant or stable organic matter (40-60 percent), also referred to as humus.
Organic matter may be divided into aboveground and belowground fractions. Above ground organic matter comprises plant residues and animal residues; below ground organic matter consists of living soil fauna and microflora, partially decomposed plant and animal residues, and humic substances.
Read Also: Organic Matter Decomposition in Soil
The C: N ratio is also used to indicate the type of material and ease of decomposition; hard woody materials with a high C: N ratio are more resilient than soft leafy materials with a low C: N ratio.
Although soil organic matter can be partitioned conveniently into different fractions, these do not represent static end products. Instead, the amounts present reflect a dynamic equilibrium. The total amount and partitioning of organic matter in the soil are influenced by soil properties and by the number of annual inputs of plant and animal residues to the ecosystem.
For example, in a given soil ecosystem, the rate of decomposition and accumulation of soil organic matter is determined by such soil properties as texture, pH, temperature, moisture, aeration, clay mineralogy, and soil biological activities. A complication is that soil organic matter in turn influences or modifies many of these same soil properties.
Read Also: Roles of Microorganisms in Organic Matter Transformation
