Chair:Francis Rayns (CAWR)
Overall aim: to enable farmers/growers to have the knowledge of how to build carbon in their soils, both improving their farms and sequestering atmospheric carbon.
Session summary
Laurence Smith (ORC) concentrated on Greenhouse Gases (GHG) and climate change. Laurence discussed how there is strong evidence to show that organic farming can increase Soil Organic Matter (SOM) and that organic systems were losing less carbon than conventional. Critical is the use of legumes and livestock manures in agroecological systems which can also lead to greater amounts of soil carbon, but the greatest gains can be made through permanent pastures.
Grower, Iain Tolhurst talked about building soil carbon at Hardwick – an interaction with biodiversity – feeding people and planet. Iain spoke of functional agricultural biodiversity and the need to understand the way your whole farm works in order to work with the environment so that it is possible to reduce carbon emissions as well as sequester carbon.
Ed Revell of Swansea Biochar spoke on soil carbon influencing factors, the creation of stable and labile soil carbon and the vital role biochar can play in returning carbon to our soils.
Key conclusions
Ed Revill
The discussion that followed the presentations brought out the following points:
- Large potential for climate change mitigation through soil carbon sequestration.
- Prediction of gains/losses difficult.
- Organic systems provide opportunities for carbon storage through mixed farming and woodland.
- Benefits may have been overestimated in some cases.
Individual speaker presentations and abstracts
Laurence Smith (ORC): Soil carbon sequestration and organic farming – a review of the evidence
With the recent interest in the potential for agriculture to capture atmospheric CO2 , through the accumulation of soil carbon, measurements in this area have been viewed as increasingly important. Promoting soil health and encouraging the development of soil organic matter have always been central tenets of the organic approach, and the potential contribution of organic systems to this area has been of considerable interest. Practices that have been shown to increase soil organic matter, such as the use of organic fertilisers, fertility building leys with legumes and cover crops are commonly found on organic farms and a range of long-term field trials have found higher organic matter contents in organically managed soils. In addition to storing carbon, higher levels of soil organic matter can enhance the nutrient buffering capacity, water holding capacity and microbial activity within soils and help to increase the soil’s fertility. This presentation will provide an overview of the current evidence in this area highlighting the potential role of organic practices for the maintenance of soil carbon and soil health.
Improvements to soil carbon have to be viewed within the whole system of the farm. It is undoubtedly challenging to improve soil carbon in horticulture, without bringing in large amounts of organic matter, often sourced from conventional farms. You need to look at the whole farm and see where you can build long term carbon. Features such as woodlands, hedges, shelter belts, beetle banks and field margins will be the most productive in terms of soil carbon accumulation, with more modest amounts possible within the actual growing land, primarily through the use of green manure fertility building leys and the possible addition of composted wood chips. So you will need to consider incorporating more of these features without reducing your crop yields. To justify the inclusion of trees and other hard carbon features you have to look at the additional benefits: shelter, increased biodiversity to control pest and disease problems, enhanced soil microbial activity etc. It is important to have an idea as to what the carbon picture really is upon your farm, so do a whole farm carbon analysis. Regular soil analysis for carbon is essential and you will need to do this for many years before you get to see any real changes. We have a duty to ensure that we are not depleting our carbon reserves and are managing to maintain and increase the carbon long term.
Human interaction with soil very often results in the release of soil carbon with adverse consequences for both soil and climate. It is vital that we understand concepts such as soil aggregation and that we change the ways that we interact with soil and soil carbon in particular. When the factors which influence soil carbon are understood and applied to cropping systems it becomes possible to produce crops in ways which firstly minimise the release of soil carbon, secondly optimise carbon draw down (through optimising plant photosynthesis) and thirdly optimise the retention of carbon in soil. Factors which influence the retention of carbon in soil can be divided into those which influence soil biology (for example soil moisture) and those pertaining to different forms of carbon compounds in soil. I will discuss soil carbon influencing factors with reference to my own market garden which combines biochar producing stove and heating systems with a coppice producing alley cropping system, using no walk, minimum dig beds to produce mainly vegetable crops for local sale and coppice for use in the biochar producing stove systems. Rather than digging the biochar into the soil, as is usually done, it is then returned to the cropping area in a mulch.
