Current Agriculture: Soil organic matter

Agriculturists since ancient times have recognized significant benefits of soil organic matter to crop productivity. These benefits have been the subject of controversy for centuries while some are still debated today.

Many of the benefits of soil organic matter have been well documented scientifically, but some effects are so intimately associated with other soil factors that it is difficult to ascribe them uniquely to the organic matter. In fact, soil is a complex, multicomponent system of interacting materials, also the properties of soil result from the net effect of all these interactions.

One of the major problems in communicating in the field of humic substances is the lack

of precise definitions for unambiguously specifying the various fractions. Unfortunately, the terminology is not used in a consistent manner. The term humus is used by some soil scientists synonymously with soil organic matter, which is to denote all organic material in the soil, including humic substances. The term humus is frequently used to represent only the humic substances.

The term soil organic matter is generally used to represent the organic constituents in the soil,

including undecayed plant and animal tissues, their partial decomposition products, and the soil biomass. Thus, this term includes:

1. Identifiable, high-molecular-weight organic materials like polysaccharides and proteins,

2. Simpler substances like sugars, amino acids, and other small molecules,

3. Humic substances.

It is likely that soil organic matter contains most if not all of the organic compounds synthesized by living organisms.

Soil organic matter is frequently said to consist of humic substances and nonhumic substances.

Nonhumic substances are all those materials that can be placed in one of the categories of discrete compounds such as amino acid, sugars, fats and so on. Humic substances are the other, unidentifiable components.