When it comes to soil organic matter, the classic method of fractionating into humic acid, fulvic acid, and humin has been ascertain for several of decades, but is no longer considered important due to the fact that the fractions are artificially defined and does not exist in soils. However, this method of fractionation does not produce chemically discrete soil organic matter fractions, but, rather, fractions that are heterogeneous and non-reproducible.
A more
biologically and agriculturally meaningful method of describing soil organic
matter is by way of dividing it into various pools which are sorted by how
easily the material is decomposed such as active or labile, slow or
intermediate and passive or stable. Pools, which have actual measurable organic
matter components, are theoretically separate entities and are more concisely
designated by way of fractions. This method of soil organic matter
classification is far more commonly used in soil studies now than the outdated
measurements of humic and fulvic acid separation.
Active and labile fraction
In a view general, younger organic material, from recently deposited roots and residue, dead organisms, or waste products, is the most biologically active form of fraction of the soil organic matter; this simply means that it serves as a food source for the living soil biological state. The younger fraction is also seen as the labile soil organic matter fraction, indicating that it is more readily decomposed than the passive or stable fraction. Generally, this fraction of the soil organic matter is less than little duration.
In active
friction, there are many ways to measure it, but one of the most commonly used
methods is to measure the particulate organic matter. Particulate organic
matter is known as the microbial active fraction of soil organic matter. The
reason that particular organic matter has become so frequently used is that it
has been shown to have a strong response to management operation decisions,
such as tillage, residue handling and levels, and crop rotation. There are a
number of different ways to measure and ascertain particulate organic matter,
but they all rely on separation techniques that are based on the size as well
as density of the soil organic matter material.
Passive and stable fraction
Most soil organisms help in the process of decomposing plant and animal tissues. During this process of plant and animal decomposition, chemical transformations take place, creating new presence of organic compounds in the soil. After years or decades of these transformations, the original organic materials are transformed into chemically complex, nutrient-poor compounds that few microbes can degrade. These compounds are known to be as passive or stabilized and can make up a third to a half of soil organic matter. Such passive or stabilized materials are what are commonly known as humus or the stable fraction.
The stable
fraction does not contain many nutrients, and by this reason, is not directly
important for soil fertility. However, the stable humus fraction of soil is
very chemically reactive and contributes to the soil net chemical charge, which
is known as the cation exchange capacity and anion exchange capacity. In this
manner, humus temporarily and reversibly covers plant nutrients in the soil,
preventing them from leaching, so that they are available for plant uptake. The
stable fraction also modifies and stabilizes toxic materials in other for them
to be less reactive or dangerous. Finally, the stable fraction enhances soil aggregation
that reduces a soil vulnerability to erosive forces and thereby reduces soil
loss which is caused by erosion.
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