Can biochar improve paludiculture profits?

Wet farming or paludiculture is a sustainable farming system that involves the cultivation of crops under wetland conditions. Through wetter management practices these farming systems offer promising opportunities to reduce CO2 emissions from lowland peat areas that are drained for agriculture. The wetter peat management supresses peat oxidation and therefore reduces CO2 emissions to the atmosphere.

Without wetter management and continued drainage these areas which occupy an approximate 250,000ha across the UK could continue to experience up to 2cm of peat loss per year.

Whilst paludiculture in the UK is still in its infancy, there are a number of UK trials cultivating a wide variety of crops such as celery, elephant grass (Miscanthus) for bioenergy, common reed for thatching and bulrush for the sustainable textile industry. Although more sustainable, without additional financial support from the government, paludiculture does not currently stack up financially compared to the business-as-usual high value cropping farming models (e.g. growing lettuce) that rely heavily on drainage practices. This is where biochar could play a significant role in bridging this economic disparity, could also contribute towards greenhouse gas removal and improve overall paludiculture adoptability by farmers.

So what is biochar?

Biochar is a charcoal-like substance produced by the pyrolysis (i.e. high temperature but no oxygen) of biomass, such as agricultural waste or forestry residue. It has a very high carbon content, comprising more than 65% carbon and is largely resistant to decomposition, making it an ideal tool for long-term carbon storage.

Integrating biochar with paludiculture – A Paludiculture Exploration Fund project.

In the context of paludiculture, biochar applications could allow for an additional source of income from carbon financing. Our understanding as to which biochars are best suited for paludiculture, how they behave in these environments and which approach is most cost-effective is limited. In light of this our project at the UK Centre for Ecology & Hydrology (UKCEH) aims to:

1. Identify application methods that can be integrated with minimal investment.
2. Identify the most cost-effective biochar that can enhance revenues from carbon financing further.
3. Maximise carbon finance and product market revenues by establishing the maximum biochar amendment rates, either in a single or in successive application, assessing the potential for biochar to suppress methane emissions, and any agronomic benefits.

Identifying the most cost-effective biochar.

A high stability biochar, produced at very high temperatures, is often more resistant to decomposition in the soil but is more costly than a lower stability biochar, which is produced at lower temperatures yet less resistant to decomposition in the soil. However, because paludiculture offers an anaerobic environment with supressed decomposition rates, could it be that a lower stability biochar, that is cheaper to produce, is just as resistant to decomposition as a higher stability biochar under these wetter, more stable environments?

To help answer this question, we at UKCEH are running a national scale experiment, at nine paludiculture sites across the UK, to quantify biochar losses to decomposition.

We used a litterbag method, where we placed a known quantity of each biochar type (Low, Medium and High stability) along with two labile carbon sources (fresh biomass - not charred, we used red bush tea and virgin wood) into small mesh bags that look very similar to a tea bag (see photograph below). This method will allow us to quantify decomposition rates, biochar mass loss and stability decay over time with periodic sampling.

The litterbags were deployed across all sites in August 2023 by placing the litterbags just below the soil surface. At a subset of sites we deployed litterbags onto peat that is drained and will continue to be drained for the duration of the project. This will allow us to compare biochar resistance to decomposition in a wet and dry peat environment.

How are the Great Fen involved?

The Great Fen is supporting this national-scale litterbag experiment by hosting the litterbags at two sites: its current wet farming test beds, and another location where the water level is deeper below ground, along with continued on-site measurements from the Wildlife Trust for Beds, Cambs and Northants.

Collaboratively sixty litter bags were deployed across both of these sites on August the 16^th by Jenny Rhymes (project lead - UKCEH), Henry Stanier (monitoring & research Officer, Wildlife Trust) and Nicky Hennessy (senior reserves officer, Wildlife Trust), along with soil moisture and water table depth monitoring equipment. In just a couple of hours the litterbags were in and all we have to do is wait until it is time to dig them back out for analysis.

In the meantime, for more information, check out our webpage.

Dr Jenny Rymes (Biochar project lead, UKCEH)