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

Summary

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 fractions. 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 directly 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 farm 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 structure,chemistry and biology will be done and the effects of the manure treatment will be studied after the first transition period of 2-3 years.
Trials will be done on less productive, recently cultivated
soil to reveal the effect of the digested versus the non-digested manure as a soil conditioner. Soil
respiration, enzyme activities and humus fractionations will be measured. Pot experiments with earthworms will bring more detailed knowledge about these key species, and additionally mites and collembolans will be recorded.
Project partners: Bioforsk, Århus University Denmark, FiBL Switzerland,Biodynamic Research Association Sweden, Norwegian farmers' unions, Norwegian Agricultural Extension Service.