6 kg of copper per year and per hectare in organic farming, 3 kg in biodynamic farming ... Doesn't this heavy metal pollute our soils?
The main treatment products used in organic farming are based on copper, an element naturally present in nature and thus logically permitted. Nevertheless, copper, like all heavy metals, doesn’t degrade and cannot be eliminated. Rather, it accumulates in the upper layer of soil. Deep-rooting vines avoid this area of high concentration. However, uprooting these vines to put in other crops often leads to failure. Copper, which is sometimes used in large quantities, destroys soil microflora and aquatic fauna, affected by erosion and runoff. In high doses, it becomes phytotoxic, with a varying tolerance threshold according to the species of plant. Conversely, copper is also one of the essential minerals that plants require - a nutrient, like water or oxygen. It has a role to play in a multitude of enzymatic systems, such as photosynthesis, during which it promotes nitrogen fixation, but also respiration, nutrition, fertility and detoxification. Lack or excess of copper are thus equally harmful to the successful development of plants. The optimum concentration is thought to be between 2 and 30 mg per kilogram of dry matter* in the aerial parts of a plant. What, then, would be the perfect dose to spray on a vine, in accordance with the grape variety, to ensure that it can act fully on the plant, be fully assimilated and digested and thus not pollute or deplete the soil? Recent studies place this figure at 30 to 100 g per hectare per year** - certainly well below the 6 kg (or soon-to-be 4 kg) of copper per hectare per year permitted by the various standards, organic or otherwise!
Finding suitable alternatives for the future remains a priority. Infusions, essential oils (which we already use for more than 10 years), decoctions, purines, macerations...? Likely accompanied by a light but accurate dose of copper, to ensure we don’t starve our vines, hindering their metabolism. New precision experiments are in the pipeline…
* Plant growth as a function of copper concentration in dry matter, Reuter and Robinson, 1997 - ** Aurea Technical Meetings, November 2017