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Importance and Direct Methods of measuring Soil Organic Carbon

Davidokul — Thu, 15 Apr 2021 17:11:52 +0000

By David Okul

The implementation of international carbon trading has made the measurement of carbon important to the global economy. In pastoral rangelands, no meaningful way of measuring carbon has been identified. Common carbon sinks include oceans, soils, and vegetation.

Soil organic carbon is an indicator of healthy and fertile soils. Carbon is the 15^th most abundant element on the earth’s crust, and fourth in the universe (after hydrogen, helium, and oxygen). On the human body, it is only second to oxygen.

Massive amounts of carbon are stored in the soil in two general forms: inorganic and organic. Inorganic carbon arises from the parent weathered rock, while organic carbon results from living or decomposing carbon compounds. However, the measure of productive soils can be captured from the soil organic carbon content.

Changes in Soil Organic Carbon take a few years and it is difficult to keep track of the trend. Regardless, frequent monitoring using a consistent methodology may help detect changes.

Why should we measure soil organic carbon?

Carbon is perhaps the most important parameter for healthy soil. Keep in mind that plants don’t absorb carbon from the soil but the atmosphere. Instead, the carbon in soil contributes to soil nutrients by adsorbing and desorbing nutrients and providing habitats for microorganisms. In short, measuring SOC helps in assessing the soil’s health. Other reasons for measuring soil organic carbon are:

It is an indicator of the water holding capacity of soils: More SOC means higher water holding capacity
Fight against climate change: As the second most important sink for carbon (after oceans), measuring SOC would help in monitoring the absorption capacity of soils.

Analytical tests for determining total soil organic carbon in soils

In general, methods of measuring soil organic carbon can be classified into two; wet digestion and dry combustion. In wet digestion methods, carbon is oxidized using chemicals while dry combustion methods involve the thermal decomposition of carbonate materials to generate carbon dioxide. Examples of wet methods include Walkley and Black and Photometric methods; while dry combustion includes ignition test and dry combustion.

1. Walkley and Black Method

The method relies on the oxidation of potassium dichromate (K₂Cr₂O₇) that is acid catalyzed. The heat from the dilution raises the temperature to induce substantial oxidation of carbon to carbon dioxide.

A modified Walkey and Black Method called Meibus uses the same procedure but includes sulphuric acid with K₂Cr₂O₇.

2. Photometric Method

Potassium dichromate (K₂Cr₂O₇) and sulphuric acid are added to the soil. After cooling for 1 hour, distilled water is added. The solution is measured using a spectrophotometer with varying concentrations of sucrose solution

3. Gravimetric method – loss on ignition (Ignition Test)

Soil samples are subjected to calcinations for 5 hours at 400℃. Then, samples are weighed and the difference in mass corresponds to soil organic matter.

4. Dry combustion

Soils are pre-treated with hydrochloric acid to remove inorganic carbon. The soil sample (often 30mg) is placed in a capsule and combusted at 975℃. It uses an automatic analyzer with a thermo conductivity sensor detector (TCD).

Key discussion points

Some of the takeaway points of the different methods of measuring SOC are:

Walkley and Black Method is relatively easy and cheap, but inaccurate
Generally, wet digestion methods tend to underestimate carbon stocks while gravimetric methods tend to overestimate.
Additionally, wet digestion methods use potentially dangerous chemicals such as chromium which could be toxic.
The most common measurement of SOC is the ignition test of soil organic matter. However, it is not an accurate measure as carbon makes between 50 and 58% of the soil organic matter.
Most organizations (including IPCC) favor dry combustion over the other methods of measuring soil organic carbon
Indirect methods of measuring soil organic carbon take less time but are less accurate.

Additional reading

Quantification of Soil Organic Carbon – Comparison of Wet Oxidation and Dry Combustion Methods

A protocol for measurement, monitoring, reporting, and verification of soil organic carbon in agricultural landscapes

David Okul is an environmental management professional with over 10 years experience on donor projects, conservation, forestry, ecotourism, and community-based natural resources management. When not working on environmental projects, I spend my time writing for Silvica on a variety of topics.

The post Importance and Direct Methods of measuring Soil Organic Carbon appeared first on Silvica: Blog for Sustainable Development .

Existing Carbon Markets in the World

Davidokul — Fri, 02 Apr 2021 14:41:49 +0000

By David Okul

Climate change is a major problem in the modern world. It is caused by greenhouse gas emissions; carbon is a major GHG. The atmosphere is one. Therefore, it doesn’t matter where emissions are released or absorbed. The world attempts to address the challenge of climate change by strategies like the Paris Agreement.

Carbon trading is among the common strategy used to tackle climate change.

Carbon markets attempt to address climate change by putting a price on carbon. The currency for carbon trading is a tonne of Carbon dioxide or GHG equivalent (CO2e). A carbon credit refers to either a permit to emit 1 tonne of carbon dioxide equivalent or removal of a carbon dioxide equivalent from the atmosphere.

Article 6 of the Paris Agreement provides a foundation for market-based climate measures approaches. The existing carbon markets can be categorized into two the regulatory compliance and voluntary carbon markets. As such, two types of credits exist including Voluntary emissions reduction (VER) and Certified emissions reduction (CER).

Regulatory Compliance Carbon Markets

As the name suggests, the regulatory compliance markets use the law to account for greenhouse gas emissions. It is regulated by mandatory national, regional, or international carbon management regimes.

In the compliance markets, offsets of a similar program have the same price based on the dynamics of supply and demand. The World Bank tracks the countries or regions that have implemented the compliance programs through the World Carbon Pricing Dashboard.

The following are examples of regulatory compliance carbon markets:

Kyoto Protocol: Three Kyoto Protocol mechanisms are important for the regulatory markets including clean development mechanism (CDM), Joint Implementation, and EU Trading Systems. According to the CDM website, there are over 7,000 such projects in the world. Unlike CDM, Joint Implementation takes place in a country committed to reducing emissions. Examples of Joint Implementation Projects are listed by UNFCCC.
The European Union Emissions Trading System: It is the world’s first and biggest carbon market. It works using the cap and trade principle.
California Emissions Trading System: Launched in 2013 and helped to reduce California GHG by over 5% in 2017. The official website is found here.
Australia Emissions Trading System: Following the Clean Energy Act in 2011, Australia put a price on carbon emissions. The carbon price was effective until 2013 when the scheme was replaced by Emission Reduction Fund, which was not effective in reducing emissions.
British Columbia Emissions Trading System:
The New Zealand Emissions:
A comprehensive list of all countries with carbon taxes and ETS (by 2015) can be found in this article here:

Voluntary Carbon Markets

As the name suggests, voluntary carbon markets include carbon credits used for voluntary purposes instead of regulations. Typically, corporate social responsibility is a key driver for voluntary carbon markets. There is no centralized voluntary carbon credit market as project developers can directly sell credit to buyers, brokers, or retailers.

The sale is voluntary markets are governed by standards, which create methodologies to define and certify projects. Some common standards used in the market include the following:

Verified carbon standards (VCS)
Plan Vivo
The Gold Standard
The American Carbon Registry
Climate Action Reserve
Verified Carbon Standard Program

Each of the standards uses different methodologies for measuring and verifying emission reductions.

Project developers use the standards to turn ideas into projects. Examples of common projects for voluntary carbon markets include REDD+ projects. Like in CDM, voluntary projects can be categorized into industrial gases, energy efficiency, renewable energy, forestry, methane reduction (from coal, landfill, and livestock), and others.

A food company may want to buy credits from a project that promotes sustainable soil techniques while another company may wish to support projects that support rural community livelihoods. The beauty of the voluntary carbon market is that it allows companies to support their cause.

The price range is variable from 0.3 cents per credit for renewable credits to hundreds of dollars for projects that can lock away carbon for thousands of years (e.g. mineralization projects).

Compliance or voluntary carbon markets

The basic idea of carbon markets and trading is simple, ‘by paying someone else to reduce/absorb greenhouse gasses emission somewhere, the buyer of the offset can compensate for his/her emission’. In practice, there are various complexities, for example in methodologies of accounting for carbon and leakages.

Regardless, existing carbon markets provide an avenue for addressing the pertinent problem of climate change. While the compliance markets provide for ‘assured’ reductions, voluntary markets offer great flexibilities for communities and organizations interested in carbon trading.

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