Soil microbial dynamics in organic (biodynamic) and integrated apple orchards

Biodynamic (organic) and integrated apple orchards can differ in their soil chemical and microbiological properties which may have implications for disease control and long-term soil fertility. Soil samples were collected from three different apple orchards (each with biodynamic and integrated plots) during three different seasons. Physical and chemical characteristics of the soils under the two management systems did not show clear differences. Basal respiration and microbial biomass were higher in organic farms, while the metabolic quotient in organic farms was lower (or equal in one case) to that of integrated farms. There were also seasonal variations. Principal component analysis of the DGGE banding patterns of dominant fungal communities revealed no influence of the farming practices. Analysis of the bacterial communities with the COMPOCHIP microarray showed that certain probes targeting bacteria known to be degraders of biocides were predominantly found in integrated farming plots, while no difference between the two management practices concerning the presence of plant growth promoting rhizobacteria was evident. In conclusion, despite the reduced use of chemicals in integrated farming (compared to conventional), soil microbial properties (CO2 production and biomass) were different to those found in biodynamic farming, while the microbial spectrum did not significantly change.