In organic and biodynamic agriculture, and especially in viticulture, copper is recognised as a natural fungicide against downy mildew. However, the applied copper is leached into the soil by precipitation, where it has low mobility and accumulates over the years. The current permitted application averages 4 kg of copper per hectare per year. Although the permissible dose has been reduced several times in recent decades, it is still important to study the ecotoxicological properties of copper on soil life and soil quality. This is especially relevant because there is currently no natural alternative to copper as a fungicide in organic and biodynamic agriculture.
Figure 1: Overview of copper doses used in 15 studies on the influence of copper dose on soil quality; data in kilograms of copper per hectare and year.
The meta-analysis concludes that, in terms of the effect of the applied dose, copper levels above 200 kg per hectare per year are problematic for soil health and the soil organisms that have been studied. This corresponds to 50 times the dose currently approved by the European Commission. According to the authors of the study, soil functions and performance are maintained with an application of 4 kg of copper per hectare per year. A supplementary study by the European Union's Copper Task Force also found no negative effects on soil quality and soil organisms at an applied rate of 4 kg of copper per hectare per year.
In terms of the accumulation effect in the soil, harmful effects on soil organisms were found above 200 kg of copper per hectare.
The researchers point out several data gaps in the studies examined. For example, no data are available on the influence of copper on larger arthropods such as insects, spiders and millipedes. In addition, the studies do not usually represent real-life conditions. Whereas in viticulture several doses of copper are normally applied per year (chronic contamination), the studies mostly examined very high doses over shorter periods (acute contamination).
The authors of the study call for further research on the topic to close existing knowledge gaps. In particular, chronic contamination with lower copper doses should be investigated instead of acute contamination with high copper doses. In addition, future studies should cover as many soil types as possible, including soils with historical copper contamination, in order to better generalise the possible conclusions.
Figure 2: Overview of the effect of copper dose (top) and copper accumulation (bottom) on different soil organisms; horizontal lines reflect the tested copper doses. Red dots denote the thresholds above which adverse effects on the different soil organisms were found. The pink line indicates the copper dose of 4 kg per hectare per year currently permitted by the European Commission.
According to the authors of the study, adverse effects on soil health only occur at 50 times the currently permitted annual copper dose. In many wine-growing areas, however, copper has been accumulating in the soil for decades. Moreover, 50 years ago the permissible copper dose was many times higher than today. It can therefore be assumed that many wine-growing areas currently exceed a soil copper content of 200 kg per hectare, with consequences for soil organisms and soil quality.
Many questions are still unanswered, for example the retention time of copper in the soil or a possibly harmful effect on insects and spiders. Finally, it is also important to make farmers aware of the issue of copper.
Biodynamic agriculture promotes soil health, which in turn means less pathological pressure on the vines. In many cases, the dosage of the products used can therefore be reduced and soil quality can be preserved in the long term.
Details of the original research paper
- Authors: Karimi, B., Masson, V., Guilland, C., Leroy, E., Pellegrini, S., Giboulot, E., Maron, P-A., Ranjard, L.
- Title: Ecotoxicity of copper input and accumulation for soil biodiversity in vineyards
- Journal: Environmental Chemistry Letters 19, 2013-2030 (2021)
- Link: https://doi.org/10.1007/s10311-020-01155-x
- Study summaries on soil quality and stress resistance in biodynamic viticulture
- Risk assessment on copper-based pesticides by the European Food Safety Authority (EFSA)