Biochar production from agricultural biomass such as rushes can yield monetary benefits for farmers and has the potential to reduce emissions from slurry management.
Several potential benefits arise from the conversion of biomass into biochar, and landowners are encouraged to shift from spraying their rushes to cutting and baling them.
The Biomass to Biochar for Farm Bioeconomy EIP-Agri project looked at how unutilised agricultural biomass can be used to produce biochar under the lead of Bernard Carey.
Biochar, which is a charcoal-like substance, was used on farm as feed input and a slurry additive to reduce greenhouse gas (GHG) emissions and to increase soil carbon storage.
From rushes to biochar
Utilising rushes for biochar production offsets the cost of traditional rush management methods, which typically involve cutting or mulching and leaving them to decompose, Carey said.
The significance of biochar is, he said, that it has the potential to provide farmers with the means of closing the nutrient loop by using it as an additive to bedding, feed and slurry.
As part of the four-year project, rushes were cut in Co. Clare which were then integrated into current agri-environmental schemes.
Based in a Hen Harrier Special Protected Area (SPA), the idea was to cut strips in the field rather than clearing the field while minding the conservation interests of the sites.
Through a process called pyrolysis, biomass such as field rushes, bracken, and scrub vegetation was heated in a low-oxygen environment at temperatures ranging from 400°-800°.
A mobile pyrolysis machine was filled with baled rushes, hazel, bracken, and gorse, while there is no displacement of food production using unutilised biomass.
Emissions reduction
Biochar from rushes was added to slurry tanks in a two-month trial and a follow-up lab repeat study saw the most promising methane reduction of 33%, compared to other biomass.
When added to silage, rush biochar improved feed efficiency, reduced GHG emissions, absorbed toxins and pathogenic enzymes in the rumen and gut of cattle, the project lead said.
Furthermore, the project also yielded a reduction in ammonia emissions when biochar was used to coat urea, and resulted in better growth rates when rush biochar was added to compost.
The standard practice of cutting and mulching rushes and allowing them to naturally degrade back into the land results in 36kg of carbon dioxide equivalent (CO2e) emissions, he said.
The cutting and baling of rushes, including the diesel required for farm machinery, and either letting the bales degrade or use them for bedding leads to 141kg CO2e.
However, by cutting, baling and converting rushes into biochar -404kg CO2e emissions are being sequestered. When biochar is applied to soil, -397kg CO2e are sequestered.
Emissions from slurry in the standard practice scenario produces 1,002kg CO2e, while by adding biochar at a rate of 10%, this reduces the global warming potential (GWP) to 179kg CO2e.
Applying slurry to the land without any biochar yields a GWP of 23,436kg CO2e, while with biochar this figure is at 3,734kg CO2eq, key life cycle analysis (LCA) findings show.
Potential payments
There are two immediate income streams to consider, Carey said, the first of which is the sale of the rushes which can “fetch anywhere from €10 to €20 per bale”.
In addition, once these rushes are transformed into biochar, he said there is the possibility of receiving a top-up payment for the carbon they sequester.
The potential emissions reduction from biochar in slurry might be quantifiable in future and could lead to payments for lower GHG emissions from slurry management practices.
Additionally, the improved quality of slurry or farmyard manure resulting from the addition of biochar can reduce fertiliser costs when applied to the land, Carey added.
In terms of ecosystem services, he said landowners can receive payments for maintaining habitats for wildlife and contribute to better water quality by avoiding rush spraying.
However, quantifying the monetary value of these ecosystem services can be more challenging due to their multifaceted nature, the project lead told Agriland.
Carey said it would be great to have a results-based system which might be part of a bigger agri-environmental scheme such as the Agri Climate Rural Environment Scheme (ACRES).
In such a system, he said, biomass could be managed and grasslands could be harvested and converted into a biochar payment for farmers for every tonne of biochar produced.
The idea is to potentially export the ecosystem services from the west, where there are a lot of rushes and marginal land, to the east coast to reduce their emissions, he said.
Every year, over the course of the project, there was an opportunity to harvest rushes, however, further research needs to be carried out by research institutes such as Teagasc, he said.