Effects of anaerobically digested manure on soil fertility - establishment of a long-term study under Norwegian conditions (SOILEFFECTS)

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The project SOILEFFECTS will identify potential risks and benefits for soil fertility when animal manure is anaerobically digested for biogas production. In systems with preferably closed cycles of nutrients and organic matter, such as organic farms, soil fertility cannot be easily maintained by purchased nutrients, and manure quality is crucial. Anaerobic digestion of animal manure for biogas utilization decreases the amount of organic carbon (C) applied to the soil, especially easily degradable C fracti ons. This may affect soil biology, for instance because earthworms and microorganisms compete about this C as a source of feed. Less earthworm activity would impact negatively soil structure and fertility. Less C application to the soil may also more dire ctly affect soil physiochemical characteristics, because soil organic matter (humus) is an essential component of cultivated soil, heavily impacting soil structure, quality and fertility. A long-term experiment will be established on Tingvoll research fa rm (organically managed), where a biogas plant is built in 2010 to digest the manure from the herd of 25 dairy cows. Initial characterization of the soil biology, chemistry and physics will be done and the effects of the manure treatment will be studied a fter the first transition period of 2-3 years. Trials will be done on fertile and on less productive, recently cultivated soil to reveal the effect of the digested versus the non-digested manure as a soil conditioner. To test the digested and non-digested manures in a stressed system, the fertile topsoil will be removed on half of the plots. Soil respiration, enzyme activities and humus fractionations will be measured. Pot experiments with earthworm will bring more detailed knowledge about these key speci es, and additionally mites and collembolans will be recorded. Project partners: Bioforsk, Århus University Denmark, FiBL Switzerland, Biodynamic Research Association Sweden, Norwegian farmers' unions.