The annual Irish composting and anaerobic digestion conference took place in Kildare last week and provided some food for thought.

In the age of climate change awareness and with the Common Agricultural Policy set for significant reforms, the topic of how agriculture can be part of the climate solution was widespread among delegates.

Irish soils have an important role in carbon sequestration and the question was posed to see if Irish farmers could be supported to help further develop this under the new CAP.

Arjen Brinkmann of the BVOR (Dutch Association of Biowaste Processors) spoke at the conference on how compost can aid carbon sequestration of Irish soils.

Arjen Brinkmann and Percy Foster.

“Sequestration of carbon in soils is increasingly recognised as a relevant measure to combat climate change,” Brinkmann explained.

One way to increase carbon uptake by soils is the application of compost as compost contains a high percentage of stable organic matter.

Soil carbon credits

Brinkmann provided an insight into the Humus Projekt, which is an Austrian private scheme for soil carbon credits.

In this project, participating farmers can sell so-called soil carbon credits, equivalent to the amount of carbon they have additionally stored in their soil during project participation.

Companies wishing to reduce their carbon footprint buy the carbon credits. Started as a local initiative in 2007, the scheme now involves more than 100 farmers throughout the country.

The Austrian retailer Hofer AG (part of Aldi) is the main buyer of credits.

An important element of this scheme is for farmers to apply an initial high compost dosage of 100t/ha to 200t/ha

When a farmer starts participating in the project, a baseline measurement is carried out of the stable organic matter (humus) in his soil.

The farmer then starts working on storing additional organic matter, eg by applying organic soil improvers, planting green cover and reduced tillage.

An important element of this scheme is for farmers to apply an initial high compost dosage of 100t/ha to 200t/ha in an attempt to kickstart microbiological soil life and help the further rapid buildup of soil organic matter.

Compost

Compost contains approximately 200kg of organic matter per tonne. In biologically stable compost, 90% of organic matter is humus. Around 57% of this stable organic matter is carbon.

After one year, this equates to 100kg carbon stored, equivalent to 375 kg CO2.

With 2% organic matter degradation per annum, this results in approximately 312kg CO2 after 10 years and 225kg CO2 after 20 years.

Soil organic matter to CO2

After two to five years, a second measurement of soil organic matter is carried out.

The additional soil organic matter stored during the first two to five project years is calculated, and converted to a corresponding amount of CO2.

The farmer then receives a payment of carbon credits equivalent to 60% of this amount of CO2.

Around 150,000t of compost and digestate was used on agricultural land last year.

Five years later, another (third) measurement of soil organic matter is undertaken.

If the content is at least equal to the quantity during the second measurement, the farmer receives a second payment corresponding to the remaining 40% of the credit value.

The carbon credits price is €45/t. They are bought by local companies to offset their CO2 emissions.

Of the €45/t paid, €30 is given to the farmer and €15 is for the scheme management. Costs for soil sampling and soil analyses, as well as coaching of farmers throughout the project, are included.

Brinkmann says that the relatively high carbon credit price is acceptable to buyers because of the credible layout of the scheme and that the money will be returned locally.

The CO2 credits form an initial financial incentive for farmers but the ultimate added value is improved soil fertility and health.

Within the first five years of the project, organic matter levels were found to increase 1% to 2% per hectare with equates to between 60t CO2/ha and 100t CO2/ha.

Ireland

Around 150,000t of compost and digestate was used on agricultural land in Ireland last year.

Percy Foster of Cré explained to delegates that the organisation has set up a carbon committee to investigate carbon sequestration and to see if a similar scheme in Ireland can be set up.

For those who are not aware of the organisation, Cré is the Composting and Anaerobic Digestion Association of Ireland.

Established in 2001, the organisation is committed to growing the biological treatment sector and supports the production of high-quality outputs, assists the delivery of Government waste diversion and bioenergy targets, and promotes the creation of sustainable indigenous jobs.

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