The Crucial Role of Soil Organic Matter in Nutrient & Carbon Management

Soil organic matter (SOM) plays a vital role in both nutrient and soil organic carbon (SOC) management. It acts as a reservoir and cycling agent for essential nutrients like nitrogen, phosphorus, and sulfur, making them available to plants in forms they can readily absorb. Additionally, SOM helps sequester carbon, mitigating climate change. Let's break down its specific roles:

Nutrient Management:

• Retention: SOM provides numerous binding sites that hold onto nutrients, preventing them from leaching away due to rainfall or irrigation. This ensures sustained nutrient availability for plant growth.
• Decomposition: Microorganisms in SOM decompose organic matter, releasing nutrients like nitrogen and phosphorus in plant-usable forms.
• Cation exchange: SOM has negatively charged surfaces that attract positively charged cations (nutrient ions like calcium and magnesium), keeping them accessible for plant uptake.

Soil Organic Carbon Management:

• Sequestration: SOM stores a significant amount of carbon, thus removing it from the atmosphere and mitigating climate change. Increasing SOM content through sustainable practices like cover cropping and reduced tillage promotes carbon sequestration.
• Enhanced soil health: Higher SOM levels lead to improved soil structure, water holding capacity, and aeration, making the soil more resilient against erosion and drought. This indirectly protects and promotes the carbon stored within.

Differentiating Soil Organic Matter and Soil Organic Carbon

Although related, SOM and SOC are distinct concepts:

• Soil Organic Matter (SOM): A complex mixture of living and dead organic material, including plant residues, animal wastes, and microbial bodies. It contains various elements like carbon, nitrogen, phosphorus, and other nutrients.
• Soil Organic Carbon (SOC): The organic carbon fraction of SOM. It represents the amount of carbon stored within the organic matter and is typically measured as a percentage of dry soil weight.

In simpler terms:

• SOM is the whole pie (diverse mix of organic material).
• SOC is just the carbon slice of that pie (amount of carbon).

Further Note:

While SOM is directly measured in some cases, SOC is easier and more commonly analyzed due to standardized methods. Often, SOC can be used to estimate SOM content with a conversion factor (around 1.72 in most cases). However, this factor can vary depending on soil type and organic matter composition.

By understanding the roles of SOM and SOC, we can effectively manage nutrient availability, sequester carbon, and promote healthy soil for sustainable agriculture and a healthier planet.

Dr Murtadha Shukur thank you for your contribution to discussion

Soil organic carbon not only improves soil nutrient bioavailability but also affects soil fertility by various other mechanisms and is of central importance for the global C-cycle, which may strongly affect atmospheric CO2-concentrations. Soil organic matter significantly improves the soil's capacity to store and supply essential nutrients and to retain toxic elements. It allows the soil to cope with changes in soil acidity, and helps soil minerals to decompose faster. Soil organic carbon is a component of soil organic matter. Organic matter is primarily made up of carbon (58%), with the remaining mass consisting of water and other nutrients such as nitrogen and potassium. The amount of C in soil represents a substantial portion of the carbon found in terrestrial ecosystems of the planet. Total C in terrestrial ecosystems is approximately 3170 gigatons (GT; 1 GT = 1 petagram = 1 billion metric tons). Of this amount, nearly 80% (2500 GT) is found in soil. 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 is commonly and incorrectly used to describe the same soil fraction as total organic carbon. Organic matter is different to total organic carbon in that it includes all the elements that are components of organic compounds, not just carbon. Organic matter contributes to nutrient retention and turnover, soil structure, moisture retention and availability, degradation of pollutants, and carbon sequestration. The negative charge associated with organic matter improves the capacity of the soil to hold nutrients by improving the cation exchange capacity of the soil. It improves soil structure, porosity and soil water infiltration rate. However, soil organic carbon is a component of soil organic matter, organic carbon makes up approximately 60% of the soil organic matter, and the remaining 40% of soil organic matter contains nitrogen, calcium, hydrogen and oxygen.