The key difference between humic and non-humic substances is that humic substances include humic acid, fulvic acid, and humin, whereas non-humic substances include fats, sugars, and amino acids.
We can describe humic substances as major components in the natural organic matter in soil and water. These include geological organic deposits such as lake sediments, peats, brown coals, and shales.
CONTENTS
1. Overview and Key Difference
2. What are Humic Substances
3. What are Non-Humic Substances
4. Humic vs Non-Humic Substances in Tabular Form
5. Summary – Humic vs Non-Humic Substances
What are Humic Substances?
Humic substances can be described as a type of soil organic matter having a specific structure and a very important component in the biosphere. These substances are useful in many physical and chemical processes in soil. Typically, the organic carbon content in soil is about 62% of the total global soil carbon content. About half of this content is humic substances.
For the longest time (in the 19th and 20th centuries), humic substances were viewed through a lens of the acid-base theory that described humic acid as an organic acid and humates as components of organic matter. Therefore, humic acids were described as organic substances that can be extracted from soil and can coagulate when a strong base extract performs acidification. According to new research, humic substances are not high molecular weight macro polymers but are heterogeneous and relatively small molecular components of soil organic matter that are auto-assembled in these molecular associations. They contain different compounds of biological origin and are synthesized by abiotic and biotic reactions in the soil.
Figure 01: A Typical Humic Acid
The three main fractions of humic substances in soil are humic acids, fulvic acids, and humin. We can determine their presence and relative abundance using different lab extraction methods. For example, humic acid and fulvic acid can be extracted as a colloidal sol from the soil, and humic acid can be precipitated from the resulting solution by adjusting the pH.
What are Non-Humic Substances?
Non-humic substances include materials that can be placed in one of the categories: sugars, amino acids, or fats. Sugars or soil carbohydrates make up about 5-25% of the organic matter in the soil. This carbohydrate comes mainly from plant remains that convert into sugars, hemicellulose, and cellulose over time. However, these substances are less decomposed by bacteria, actinomycetes, and fungi. This, in turn, forms polysaccharides and other carbohydrates of their own.
Soil carbohydrates are important because they form complex polysaccharides that can bind to inorganic solid particles into stable aggregates. Moreover, carbohydrates form complexes with metal ions and also serve as building blocks for humus synthesis. Moreover, some types of soil carbohydrates stimulate seed germination and root elongation.
Furthermore, soil lipids or fats resemble a group of compounds rather than a single type of compound. For example, this group of compounds includes sterols, terpenes, polynuclear hydrocarbons, chlorophyll, fats, waxes, and resins. About 2-6% of soil humus is lipids.
In addition, amino acids also form a portion of non-humic substances. These substances can occur as free amino acids in the soil solution and in soil micropores, as proteins and peptides bound to clay minerals, as peptides and proteins bound to humic collide, as mucoproteins, and as muramic acid.
What is the Difference Between Humic and Non-Humic Substances?
Humic and non-humic substances are fractions of organic matter in the soil. These two groups contain several other types of organic compounds as members of each group. The key difference between humic and non-humic substances is that humic substances are humic acid, fulvic acid, and humin, whereas non-humic substances include fats, sugars, and amino acids.
The following table summarizes the difference between humic and non-humic substances.
Summary – Humic vs Non-Humic Substances
Humic substances are a type of soil organic matter, having a specific structure and a very important component in the biosphere. The key difference between humic and non-humic substances is that humic substances include humic acid, fulvic acid, and humin, whereas non-humic substances include fats, sugars, and amino acids.
Reference:
1. “Humic Substances: Its Toxicology, Chemistry and Biology Associated with Soil, Plants and Environment.” IntechOpen.
Image Courtesy:
1. “Humic acid” By Yikrazuul – Own work (Public Domain) via Commons Wikimedia