In agriculture, humus build-up is one of the most important means of increasing soil fertility. Humus enables the soil to store water for longer periods of time or improves the usable field capacity. In addition, humus affects yield capacity, tillage, and erosion susceptibility. Humus buildup is achieved with an increased supply of organic matter, as well as reduced removal of organic matter from the land. But what actually is humus? And what effect does humus buildup have on the greenhouse gas balance?
Introduction
In agriculture, humus is the total organic matter in the soil. Humus is further subdivided into nutrient humus and permanent humus. While nutrient humus is influenced by soil cultivation, the stable fraction of permanent humus is largely protected from degradation processes.2 Nutrient humus releases nutrients under the influence of mineralization. This includes nitrogen and phosphorus as well as carbon, which is released during dissimilation for the purpose of energy production in the form of CO2. Atmospheric CO2 can also be used to build up organic matter in the soil. From this point of view, carbon sequestration can contribute to the reduction of atmospheric CO2.
The active pool contains the biomass from bacteria and fungi and the associated degradation products with a relatively fast conversion rate of several months to years. Organic matter in the slow pool has an average residence time in this phase with a transformation rate of several decades. In comparison, organic matter in the passive pool is protected for centuries. The humus in the passive pool is consolidated by mineral compound (clay-humus complex).
Why can humus be accumulated in the REDcert/ISCC system?
Humus accumulation on agricultural soils is a major component of the IPCC (“International Panel on Climate Change”) recommendation to reduce greenhouse gas emissions and achieve the Paris climate goals.Due to the long-term sequestration of carbon in the clay-humus complex, CO2 is removed from the atmosphere. If substrate production takes place on the humus-building land, the carbon accumulation can be claimed in the REDcert or ISCC system. The crediting can be done under the item esca. With esca, other possibilities for carbon storage in soils are also considered. These include, among others, the manure bonus. In order to ensure a longer-term carbon sequestration, some points have to be considered:
- Evidence of carbon sequestration must be available.
- This can be done via a humus measurement prior to the start of the changed management practice.
- Alternatively, a credible calculation for accumulation can be provided
Carbon sequestration measurement should be done through certified agencies. In addition, samples should be retained for more than 5 years for review during an audit.
-
The improved management practices must be carried out for at least 10 years
-
Additional requirements apply to the sampling of the reference plot
- Sampling must be conducted for each field
- Smaller plots with similar climate and soil types may be grouped together
- Sampling should be carried out before field cultivation or 2 months after harvesting.
However, if the criteria are not met , the GHG savings are included as emissions in the GHG calculation. In addition, no emission savings from humus establishment can be accounted for in the subsequent 5 years.
Practical options for humus accumulation.
If the option of humus accumulation is considered, then several management practices that have been shown to have a positive impact on carbon content should be implemented. These include:
- Reduction of tillage up to the introduction of no-tillage systems (no tillage).
- Improved crop rotation (stalk/leaf crop and summer/winter crop).
- Use of catch crops (improved crop residue management)
- Application of organic soil improvers (compost, farm manures, biochar).
The above practices must have been implemented on the farm 3 years prior to potential crediting.
How is the humus accumulation calculated?
The humus content of a soil depends on the climate and the soil type of the respective reference area. For the calculation, the humus content of the reference area should be recorded before the improved land management practices are introduced. Carbon accumulation can be claimed using the following formula:
esca = (CSR - CSA) x 3,664 x 1/20 x 1/P - eB
The following table gives an explanation for the elements used in the formula:
| element | description |
|---|---|
| CSR | Carbon content of the reference area, measured in t C/ha (before extraction of the raw material on the area) |
| CSA | ctual carbon content of the reference area, measured in t C/ha (after 20 years or at the time of maturity of the plant) |
| 3,664 | 3.664 Conversion factor from C to CO2 (dividing the molecular weight of CO2 by the molecular weight of C) |
| 1/20 | Distribution of annual carbon accumulation over 20 years |
| P | Plant productivity (biomass fuel energy per unit area per year |
| eB | Bonus of 29 g CO2eq/MJ on when growing substrate on restored degraded land |
Outlook
When considering the requirements for humus build-up under the esca section in the REDcert system, a comparably good greenhouse gas saving can be achieved.
This saving can be an incentive for the farmer to contribute to reducing greenhouse gas emissions.
In return, the producer can monetize the savings in the long term.
Disclaimer
This post was orginally written in german and was translated to english via deepl.com. I tried checking the translation for errors but I did not find any. Feel free to contact me in case you want more information or you got some suggestions to improve this post. The original german source can be found at the agriportance website.