What is new in Soil Carbon Check?

When the Soil Carbon Check is performed yearly, significance can be proofed much sooner.  Moreover, many chain partners demand recent carbon data.

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.

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 CO₂. Micro-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.

At the COP21 (Paris) a 4 per 1000 increase was anticipated; so an annual increase of 0.4% per year.  On average an increase of 2 ton CO2 can be expected (depending on among others weather conditions and management). 

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.

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.

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

A content of 1% in the upper 30 cm soil represents a quantity of 37.5 tons captured CO_2, so to increase the carbon content in the soil by 1%, 37.5 tons of effective organic matter must be supplied. Suppose the average humification coefficient is 0.7, then over 53.5 tons of fresh organic matter must be supplied! Increasing the organic matter content is therefore done in small steps. Here are some measures you can take:

• Improve crop rotation. Crops such as maize, potatoes and onions take up a lot of nutrients from the soil and leave little crop residue. Crops like wheat, barley, and grasses form a lot of organic matter and thus contribute to organic matter accumulation.
• Provide additional organic matter with animal manure or compost. In the circular economy, the use of compost will become increasingly important.
• Sow a green manure crop and prevent the soil from going fallow. There are several types of green manure and their contribution to organic matter varies. The choice of green manure depends on the land, soil health and climate. More about green manures
• Leave crop residues (roots, stems etc.) on the land as much as possible after cultivation. This contributes to soil health and the build-up of organic matter and prevents erosion.
• Ensure optimal crop growth. Fertilization tailored to the crop and the soil and sufficient water are needed. Soil and crop analyses will give you indispensable insight to optimize fertilization and ensure that the crop receives exactly enough nutrients during the cultivation.

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.

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.

Organic matter retains moisture. Plots with higher organic matter content are therefore less susceptible to drought and can more effectively ‘capture’ water from rainfall.

It is food for soil organisms, therefore not only important for mineralization, but also for the resilience of the soil. Finally, organic matter improves the workability of the soil.

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.

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.

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

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.

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.

Use the link or QR-code on your report to open the Carbon Calculator. The Carbon Calculator will then start with your latest personal soil carbon data. Use this data to optimize your choice of crop or which manure/green manure/compost to apply on your fields.

The Carbon Calculator also shows the amount of carbon credits you have built up. 

Carbon Calculator