SLU news

Biogas for increased organic production

Published: 07 February 2012

Biogas – the solution for increasing production in organic farming? This was the theme of a meeting in Alnarp Jan. 31, where representatives from the Swedish organic labelling organisation KRAV, researchers from SLU and biogas-producing farmers were invited to provide information on regulations, present experimental results and discuss the practical challenges. The meeting was organized by the project “Biogas in Lundaland” in cooperation with Federation of Swedish Farmers (LRF), Swedish Ecological Farmers’ Association and SLU in Alnarp.

- Biogas is important for the climate and for the sake of jobs, said Markus Paulsson, coach at the project Biogas in Lundaland which is a collaboration between five municipalities in Scania region.

- If manure is used for biogas production and digestate is returned as fertilizer it will lead to reduced losses of nitrogen gases and carbon dioxide into the atmosphere, thus reducing the climate impact in comparison to when manure is spread directly on the ground, said Markus Paulsson.

KRAV allows digestion of certain amount conventional manure
Kjell Sjödahl Svensson, regulation responsible at KRAV (, informed about the rules for use of the digestate (also called bio-fertilizer) in organic certified cultivation. Today, digestate from biogas plants can be used as fertilizer in organic certified cultivation only if the biogas plant digests KRAV-approved fertilizers. Digestate from anaerobic digestion of crops are allowed. Digestate from anaerobic digestion of manure may be used if the manure comes from certified organic farming.

With the exception of manure from industrial agriculture, e.g. hogs, animals in cages or intensive slaughter bird production, also manure from conventional farming is allowed. Digestate from anaerobic digestion of household waste may be used if the waste meets certain certification and quality standards. Kjell Sjödahl Svensson believes that the EU needs to look at ways to digest several clean recycle products in order to get a larger portion of the nutrients returned to agriculture in the future.

Largest gain is easily accessible nitrogen
Krister Andersson is a farmer at Hagavik Farm outside Malmö. He has grown organically since 1999 and produced biogas since 2003. Crop rotation includes wheat, oilseed rape, field beans and forage (ley). The farm also produces beets. Today he uses food waste and chicken manure as substrate for biogas production. Previously, he also digested the ley harvest, but the costs of harvesting and storage made this less paid off compared to food waste and chicken manure.

The digestate is added to rapeseed, wheat and beetroot. The spread is by means of a liquid manure drill in growing crops for optimum nutrients effect and least possible odour. Storage capacity and transportation costs limit the use of the digestate to the fields that are relatively close to the farm centre. Today the biogas is used to produce electricity and consumed on the farm and partly sold to the utility company. Krister Andersson says the biggest benefit of the biogas plant is that the farm will have access to readily available ammonium nitrogen.

In field trials gave digestate best economy at 100 kg per hectare
Sven-Erik Svensson, researcher at SLU, referred to field trials conducted by HIR Malmöhus over three years in which the harvest, nitrogen efficiency and economy for digestate, poultry manure and bone meal were compared at the Hagavik Farm. The calculations showed that at a nitrogen dose of 100 kg per hectare gave the digestate the best economy. Both gross margin and the additional revenue due to fertilization (fertilizing net) was a bit lower in the use of chicken manure and lowest for bone meal. At 50 kg of nitrogen per hectare profitability was lower for all three fertilizers. It was, however, poultry manure fertilization that was giving the fertilizing net maximum. Nitrogen efficiency did not differ significantly between the three fertilizers.

Higher energy yields per hectare than RME and ethanol
According to Thomas Prade, researcher at SLU, biogas production produces higher energy yields per hectare compared with RME biofuels and ethanol. Compared with ryegrass and crop residues from a number of different crops, grass silage from ley gave most energy per hectare. Thomas Prade has compared the biogas production for an arable farm with 60 hectares and an animal farm with 100 hectares and 45 cows where all the feed comes from the farm. Crop residues, manure, feed waste and biogas substrate were used to produce biogas. The crop farm produced about 30 per cent more energy compared to the dairy farm.

More research is needed to secure soil organic matter
Anaerobic digestion to produce biogas and digestate is an important tool to address the challenges of organic farming, says Erik Steen Jensen, professor at SLU. Production of biogas leads to reduced losses of nutrients compared with spreading fertilizer directly, and it also contributes to reducing the use of fossil energy. This contributes again to a reduced carbon footprint. You also get better possibilities to manage nutrient strategically in organic farming because it is easier to add fertilizer where it is needed in the crop rotation. This also contributes to improved nitrogen uptake.

In trials at SLU higher yields ha been accomplished during anaerobic digestion of forage and crop residues compared to direct mix into the soil. Biogas production also offers the opportunity to bring in new crops in the crop rotation. More research is needed on how to integrate biogas digestion in organic production without jeopardizing the content of organic matter in soil. A new SLU project has been initiated to investigate how the management of plant nutrients can be optimized in organic cropping systems without livestock but with biogas production.

EU regulation and economy of production are bottlenecks
Two major constraints for the development of biogas production in Sweden was raised in the concluding discussion. One limitation is the current barriers to the use of certain recycling products as biogas substrate in the EU Regulation and its interpretation by the Swedish Board of Agriculture. Another factor limiting the establishment of new biogas plants in Sweden is the economy of biogas production. Should society in the future pay for the reduction of carbon and nutrient losses when waste and manure is used for biogas production?