Soil organic matter (SOM) and soil organic carbon (SOC) are closely related but distinct components of soil. SOM is a complex mixture of organic compounds derived from plant and animal residues, while SOC is the carbon component of SOM. The relationship between SOM and SOC can be expressed by the following equation:

SOM = SOC x 1.72

This conversion factor is based on the assumption that SOM contains about 58% carbon. However, the actual carbon content of SOM can vary depending on the type of organic matter present. For example, SOM derived from manure or compost may have a higher carbon content than SOM derived from crop residues.

The relationship between SOM and SOC is important for several reasons. First, it allows scientists to convert measurements of SOC to estimates of SOM, which is a more comprehensive indicator of soil health. Second, it helps to understand the fate of carbon in soil. When organic matter is decomposed, some of the carbon is released into the atmosphere as carbon dioxide, while some of the carbon is stored in the soil as SOC.

The amount of SOC in soil can vary greatly depending on the type of soil, climate, and land use. In general, soils with a higher clay content and a more humid climate tend to have higher SOC levels. Soils that are managed with practices that increase organic matter inputs, such as cover cropping and compost application, also tend to have higher SOC levels.

Increasing SOC levels in soil can have several benefits, including:

• Improved soil structure and water infiltration
• Increased nutrient retention
• Reduced soil erosion
• Enhanced soil biodiversity
• Sequestration of carbon from the atmosphere

These benefits can lead to improved agricultural productivity and reduced environmental impacts. As a result, there is growing interest in developing practices that can increase SOC levels in soil.

Dr Murtadha Shukur thank you for your contribution to the discussion

Soil organic matter consists of about 57% carbon while carbon is the primary component, soil organic matter also contains hydrogen and oxygen and is an important source of nutrients; nitrogen, phosphorus, sulphur and trace elements. The conversion factor of 1.724, based on the assumption that organic matter is 58% carbon, has been used for converting measurements of soil organic carbon (OC) into estimates of soil organic matter (OM). Foc is the Fraction of Organic Carbon in a soil, which is simply its Total Organic Carbon content expressed as a decimal fraction (e.g. 1.0% TOC = 0.010 Foc). Photosynthesis in land plants fixes atmospheric CO2 as organic carbon, which is either stored as plant biomass or in soil, or is decomposed back to CO2 through plant and soil respiration. Total soil carbon includes both organic and inorganic carbon. Soil organic carbon includes the once-living matter from plants, dead leaves, roots, and soil microbes, while inorganic carbon is mineral-based and much less responsive to management. Total organic carbon (TOC) is the carbon (C) stored in soil organic matter (SOM). Organic carbon (OC) enters the soil through the decomposition of plant and animal residues, root exudates, living and dead microorganisms, and soil biota. Carbon is the primary component; soil organic matter also contains hydrogen and oxygen and is an important source of nutrients; nitrogen, phosphorus, sulphur and trace elements.

Fraction organic carbon refers to the amount of organic carbon present in a specific fraction of the soil, such as particulate organic matter (POM), dissolved organic matter (DOM), or humus. Soil organic matter refers to the total amount of organic material present in the soil, including all the various fractions.

To convert fraction organic carbon to soil organic matter, you need to take into account the fraction's proportion in relation to the total organic carbon content. The conversion factor differs depending on the fraction you are considering. For example, if you want to convert POM carbon to soil organic matter, you would multiply the POM carbon content by a conversion factor specific to this fraction.

The relationship between soil organic matter and soil organic carbon is that soil organic matter consists of various fractions of organic carbon along with other organic and inorganic components. Soil organic carbon is the specific measure of just the carbon content in the soil organic matter.

Soil organic matter plays a vital role in soil fertility, structure, nutrient cycling, and water-holding capacity. It serves as a reservoir for nutrients, enhances soil aggregation, promotes microbial activity, and improves soil structure. Soil organic matter also contributes to the overall soil health and resilience, influencing its ability to retain water and withstand environmental stresses.

Soil organic carbon represents the energy source for soil microorganisms, and its decomposition leads to the release of carbon dioxide into the atmosphere. Monitoring soil organic carbon levels is important for assessing soil health, carbon sequestration potential, and evaluating management practices' impact on soil quality.

Overall, while soil organic matter encompasses all organic materials in the soil, soil organic carbon specifically refers to the carbon content of those materials. Both are crucial components for the functioning and health of soils.

Thank you prof for your recommendation

Dr Godwin Sabah thank you for your contribution to the discussion

Soil organisms form a complex food web, and soil organic matter is the base of the web. Most soil microorganisms use organic compounds in soil organic matter as carbon and energy sources. Some soil organisms feed directly on living roots, but most depend on dead plant matter. While carbon is the primary component, soil organic matter also contains hydrogen and oxygen and is an important source of nutrients; nitrogen, phosphorus, sulphur and trace elements. Organic matter (%) = Total organic carbon (%) x 1.72. This conversion factor assumes organic matter contains 58 % organic carbon. However this can vary with the type of organic matter, soil type and soil depth. Soil organic C regulates critical ecosystem services such as nutrient provisioning, water-holding capacity and soil drainage, soil stability, and greenhouse gas emissions that can mitigate or accelerate climate change. Soil organic carbon (SOC) depends on land management and land use. Land planning policy determines land use and management; therefore changes in both can produce a decrease of SOC. This is especially important in Mediterranean environments due to the scarcity of organic matter in soil. Organic matter within the soil serves several functions. From a practical agricultural standpoint, it is important for two main reasons: (i) as a “revolving nutrient fund”; and (ii) as an agent to improve soil structure, maintain tilth and minimize erosion. Leaving crop residues on the soil surface increases the input of carbon to the soil and retains soil moisture. Over time, stubble breaks down and contributes to soil organic carbon. The rate of break down depends on the ratio of carbon to nitrogen in the residues and the availability of nitrogen in the soil. So, soil organic matter is critical for forming aggregates, and aggregates are critical for holding water. Because of that link, there is definitely a positive relationship between organic matter and water-holding capacity. How much water-holding capacity increases depends on your soil type.