Effect of biodynamic soil amendments on microbial communities in comparison with inorganic fertilization

- Application of biodynamic preparations did not cause any positive effects.
- Farmyard manure increased bacterial PLFA and muramic acid in soil.
- Manure increased the contribution of AMF biomarker PLFA 16:1ω5 to fungal tissue.
- Straw incorporation and lower pH increased the ergosterol to microbial biomass C ratio.
- Straw incorporation also increased the fungal PLFA 18:2ω6,9 to total PLFA ratio.

Cattle farmyard manure application is an important tool for maintaining soil fertility in organic agriculture, especially in biodynamic systems. The first objective was to investigate whether application of biodynamic preparations (CMBD treatment) causes positive effects additional to those of composted cattle farmyard manure fertilization (CM treatment). The second objective was to investigate the response of microbial cell-wall and cell-membrane biomarkers to the CM and CMBD treatments in comparison with inorganic fertilization plus straw return (MIN treatment). The third objective was to re-assess conversion values from the phospho-lipid fatty acid (PLFA) 16:1ω5 to arbuscular mycorrhizal fungal (AMF) biomass as well as those from ergosterol and the PLFA 18:2ω6,9 to saprotrophic fungal biomass. Application of biodynamic preparations did not cause any positive effects additional to those of composted farmyard manure fertilization. In the CM and CMBD treatments, bacterial PLFA content was 33% higher than in the MIN treatment, whereas bacterial muramic acid (MurN) content was 55% higher. The AMF indicator PLFA 16:1ω5 as well as neutral lipid fatty acid (NLFA) 16:1ω5 were both increased by roughly 80%, as the NLFA/PLFA ratio of 16:1ω5 varied only in a small range around 3.8. This indicates negligible interference from bacteria, suggesting that PLFA 16:1ω5 is a suitable marker for AMF biomass in soil. The indicators for saprotrophic fungi, the ergosterol content and the contribution of 18:2ω6,9 to total PLFA (mol%) were 40 and 60% higher, respectively, in the CM and CMBD than in the MIN treatments. In contrast, fungal GlcN was not affected by the fertilizer treatments. An increased ergosterol/fungal GlcN ratio indicates a shift in fungal community from AMF towards saprotrophic fungi in arable soils.