Implications of on-farm anaerobic digestion for organic farming systems
Laura Clements, University of Southampton
This proposal is linked to a RELU project on 'Integrated systems for farm diversification into energy production by anaerobic digestion: implications for rural development, land use & the environment'. The aim of the current work is to look at the specific implications and opportunities of anaerobic digestion (AD) for organic farming. The theme is important for a number of reasons: diversification into organic farming is being driven by sharp growth in consumer demand, and by a trend for supermarkets and other large players to demand life cycle based carbon footprints and environmental performance indicators from their suppliers. The move to organic production places increasing demands on the supply of farm-produced substitutes for synthetic fertilisers such as manures and composts, while there are recognised safety issues associated with importing off-farm wastes. In this context the major benefit of AD for organic farming could be the provision of a consistent and quality-assured supply of organically-based soil nutrient supplements, with potential advantages over currently-used synthetic fertiliser substitutes. The energy derived from AD may be of secondary importance in terms of the farm economy, but could have a direct use in treatment and preparation of digestate-based organic fertilisers, and also offers a good 'fit' to overall concepts of sustainable farming in the organic sector.
Questions or hypotheses to be addressed
The current research seeks to address a range of questions:
• To what extent can on-farm nutrient recycling operate as a closed-cycle process in an organic farming context, and how much material must be imported? What questions does importing materials raise with respect to sources and acceptability to regulator)' criteria and public opinion?
• Can added value be gained from using digesfates from energy production through AD of energy crops, agro-wastes and/or other organic residues as substitutes for currently used organic fertiliser products?
• How does on-farm AD fit in with organic farming practices? What are the requirements for digestate products in terms of material types and application procedures? What are the particular implications with respect to crop rotation, for the management practices used in organic farming to ensure plant and animal health, and for the size of units / cooperatives?