Does digestate from biogas production benefit to the numbers of springtails (Insecta: Collembola) and mites (Arachnida: Acari)?

Energy production from biogas digestion creates a new era for organic fertilization, which is a great option and challenge for soil fertility at the same time. From biogas production large quantities of digestate occur as waste products that have to be disposed and might be used as fertilizers in agriculture to stimulate activity of soil organisms. We tested the effects of different fertilization regimes with digestate on the numbers of Collembola and mites in a three-year study in north-eastern Brandenburg, Germany. The trial was performed in a field of grain maize on slightly loamy sand with three manure variants in five blocks with five replications, each. Collembola and mites were obtained by drawing soil cores taken monthly from April to September 2010 through 2012 in three depths. In parallel to the animal sampling soil cores of 100 cm3 volume were taken to measure the soil moisture represented by the water volume of the upper 15 cm of soil. After the animals were extracted by a MacFadyen device, the numbers of individuals of Collembola and mites were counted for each sample. Although there were annual fluctuations in the maximum numbers of Collembola and mites in the three variants from year to year the results of a GLM-analysis for the whole investigation period revealed that the numbers of Collembola and mites were the highest in the fertilization variant of 100% digestate from biogas production. The numbers of Collembola and mites were significantly positively correlated with soil humidity in 2010, 2012 and for the whole investigation period in 0–5 cm soil depth as well as for all soil depths summed up, with the exception of the numbers of mites in 2012. We conclude that manuring with digestate had an augmenting effect on the numbers of Collembola and mites. This result is confirmed in the literature for the same animal groups and additionally for other beneficial soil organisms like earthworms and enchytraeids.