What is the relation between soil organic matter and soil organic carbon?

Soil organic matter is the collective term for all the material found in the soil that comes from microorganisms, plants and animals. Organic matter consists largely of complex molecules of carbon (C), oxygen (O) and hydrogen (H). It also contains other organic substances (e.g. proteins and amino acids) which include nitrogen (N), phosphorus (P) and sulfur (S).

As a guideline, carbon makes up about 50% of the organic matter, however, this percentage varies widely (between 30 and 70%). The actual carbon content depends on factors such as the origin of the organic matter and the type of soil.

Organic matter enters the soil through means such as the supply of crop residues (leaves, stems and roots), animal manure, green manuring and compost. Bacteria, fungi and other soil organisms break it down until indigestible residues remain. The decomposition process occurs in several steps involving all organisms of the soil food web. Decomposition is rapid at first and then slows down. It can take decades for freshly applied material to be fully converted to stable organic matter.

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Related faqs

What is new in Soil Carbon Check?

Soil Carbon Check is a soil test that provides unique insight into the actual amount of CO2 stored in the soil, and the development of CO2 capture over time. Soil Carbon Check is based on an organic matter determination with NIRS. Soil Carbon Check adds depth to the existing C-determination on Fertilizer Manager.

The report of Soil Carbon Check is supported by the Carbon Calculator. This handy calculator makes it possible to determine the effect on carbon capture of a crop, green manure crop or animal manure or compost. The advice that follows makes possible to optimize the carbon management for the own situation.

Why should you perform Soil Carbon Check annually?

The build-up of organic matter in the soil takes time and requires continuous attention of the farmer/grower. Soil management and mineralization by soil life have great effect on carbon capture. Especially climatic conditions, temperature and precipitation, are important here. Annual monitoring provides insight into the actual state of the soil; measuring and re-measuring the soil carbon status should (hopefully) lead to a significant increase in CO2 storage. When the Soil Carbon Check analysis is not performed yearly, significance can not be proofed. Moreover, chain partners in the agri-food sector ask for up-to-date figures on the condition of the soil. Only on the basis of up-to-date data is it possible to prove and claim sustainable land use.

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How much CO2 can the soil capture?

CO2 is captured in the soil organic material as carbon. Plants capture CO2 from the air through photosynthesis into organic matter, therefore, leaves, wood and roots form an endless storage vessel for CO2Micro-organisms are also a major source of soil organic material, however, soil life (fungi, bacteria, small insects etc.) also breaks down organic material. This causes CO2 to be released again and this is known as the carbon cycle.
CO2 capture in organic matter therefore depends on the type of organic matter: stable organic matter contains more carbon than fresh organic matter. The activity of the soil life is important for the degree of degradation. Carbon Check provides insight into the amount of carbon captured.

How do you calculate how much CO2 is captured in organic matter?

To calculate climate impact, soil carbon capture is converted to CO2. To do this, a factor of 44/12 = 3.67 is used (mole mass CO2/mole mass C). This means that 1 ton of soil carbon (as part of soil organic matter) matter corresponds to 3.67 tons of CO2 capture.

How can I increase CO2 capture in the soil?

Increasing soil organic material is quite a challenge. Soil often already contains a large amount of organic matter.

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What role does organic matter play in the soil?

Organic matter has several important functions in the soil. It is one of the most important indicators of soil health. Organic matter is food for all soil organisms. Because no light penetrates into the soil, soil organisms cannot use sunlight for photosynthesis as an energy source. This means all soil organisms depend on organic matter for their energy and food supply. Organic matter contributes to nutrient delivery, moisture and air management and soil structure.

How does organic matter contribute to soil health?

Organic matter affects biological, chemical and physical soil fertility. Organic matter provides nitrogen (N), sulphur (S) and other nutrients to crops by being released during the decomposition of organic matter. Nutrients like potassium (K), magnesium (Mg) and calcium (Ca) are loosely bound to organic molecules, which are weakly negatively electrically charged. They can thus hold positively charged ions such as ammonium (NH4+) or potassium (K+) to the CEC.

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What is a soil organic matter balance?

Most organic matter is stable, however, organic matter can disappear through decomposition by soil life and it is re-supplemented by the input of manure, compost and crop residues for example. The difference between supply and degradation determines whether the content is in balance. If the decomposition is higher than the supply, the organic matter content decreases and vice versa. In practice, the concept of 'effective organic matter' is often used for calculating the supply.

What is effective organic matter?

Effective organic matter is the part of the organic matter that remains in the soil one year after application of crop residues, manure or compost. In the first year after application a large part of the organic matter disappears because it is easily degradable. The contribution of this fraction to the content in the soil is therefore quite small. The contribution of the more stable fraction is greater.

Which crops should I sow to improve soil organic matter?

One crop is not the other when it comes to the contribution to effective organic matter. More about green manures.

What is the effect of global warming on soil carbon capture?

As it gets warmer on earth, the breakdown of organic matter in the soil will increase. It is therefore important to keep a finger on the pulse and perform regular Soil Carbon Check.

What is the Carbon Calculator?

The report of Soil Carbon Check is supported by the Carbon Calculator. This handy calculator makes it possible to determine the effect on carbon capture of a crop, green manure crop or animal manure or compost. The advice that follows makes possible to optimize the carbon management for the own situation.

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