Long-term copper application in an organic vineyard modifies spatial distribution of soil micro-organisms

Organic viticulturists utilize copper to prevent and reduce downy mildew (Plasmopara viticola) within the vineyard. Being a heavy metal, copper either builds up in the soil or is leached into the groundwater or taken up by living organisms. Therefore, its use impacts the environment. In organic farming there are currently no copper substitutes available and, therefore, it is necessary to understand the depth of damage that copper is inflicting on soil microbial communities over the long-term. Here a field-scale grid, 4 m by 5 m, was analyzed within a 17 year practicing organic vineyard in Southwestern Germany. Copper fractions, enzyme analyses (phosphatase, arylsulfatase, invertase, urease, xylanase), fungal analyses (ergosterol, fungal PLFA), bacterial analyses (bacterial PLFA), and microbial biomass were measured and spatial distribution maps were interpolated. Readily available and exchangeable copper fractions were higher within the vine rows and lower between them. Total copper ranged from 43 mg kg−1 to 142 mg kg−1, which is above prevention levels for Germany. In areas of high copper, a negative effect on total carbon, ergosterol, as well as phosphatase and invertase enzyme activities was observed. Tillage practices were found to be more important than copper for the distribution of carbon, nitrogen and xylanase activity within the vineyard.