Copper is one of the essential micronutrients for all living organisms, including plants, and acts as a cofactor for many enzymes involved in respiration and electron transport proteins. At the same time, at higher concentrations, it also acts as a broad-spectrum biocide.
The convenience it offers has made it easier to manage diseases, especially in organic farming, but it is also important in conventional farming because of its low cost.
In contrast to conventional farming, where there are several fungicides and bactericides available for managing crop diseases caused by pathogenic fungi and bacteria, there are few available for protecting organic crops, making copper one of the main ones. Since all of us farmers use it, it is important to be aware that the accumulation of heavy metals in the soil has negative effects on the environment, and we must exercise appropriate caution.
The prolonged use of copper for over a century has resulted in the accumulation of this heavy metal in the soil, as its residues typically remain in the top 15 centimeters. Of course, it is difficult to accurately assess to what extent the high levels of copper are due to farmers’ use of it, since copper is naturally present in the soil anyway.
However, toxicity varies from one soil to another, regardless of its concentration levels. For example, in alkaline soils where calcium is more readily available, phytotoxicity is lower, while it increases significantly as the pH decreases.
In addition, the downward movement of copper is greater in sandy soils than in soils rich in clay or organic matter, which retain it.
The problem is more serious in perennial crops, such as orchards and vineyards, since in some of them we find 40 to 50 times more copper, but also in vegetable gardens, where plant species susceptible to fungi and bacteria have been cultivated for many years.
The Risks Associated with Excessive Use of Inorganic Copper in Crops
Its intensive use has led to a range of impacts related to human health and biodiversity, and overall, there are both direct and indirect negative impacts.
Copper is toxic to an extremely diverse range of microorganisms (bacteria and fungi) and macroorganisms (protozoa, nematodes, mites, millipedes, spiders, various insects, and earthworms). In organic soils, these organisms play a very important role, ranging from the decomposition of active organic matter to the storage and release of nutrients, soil structure and stability, resistance to pathogens, and the breakdown of pesticides and other pollutants.
The problem is more acute for microorganisms, as they are generally more sensitive to heavy metals than other organisms. For example, the adverse effects of heavy metals on microbial activity and function can ultimately lead to bioturbation, which occurs when organisms stir up sediments, resulting in soil cementation.
A 1996 study by Kandeler showed that microbial biomass, enzyme activity, and the functional diversity of soil microbial communities were significantly reduced with increasing copper pollution across all soil types.
In most soils, copper residues are likely to remain indefinitely and continue to affect their health.
Elevated levels of copper can cause contamination of surface and groundwater and have significant impacts on water quality and aquatic environments if not properly managed, because, as we mentioned, under normal conditions, it cannot penetrate the soil to reach the aquifer.
Phytotoxicity
High levels of copper in the soil can cause stress in plants, reduce soil fertility, and have adverse effects on crop yield and quality. Copper compounds release ions when dissolved in water, and excessive uptake of these ions by plants usually leads to symptoms of phytotoxicity.
Factors Leading to Phytotoxicity
1) The application of highly soluble formulations (e.g., copper sulfate, copper nitrate)
2) Excessive amounts (either a very high application rate or very frequent applications)
3) The use of an acidic solution (pH below 5.5) that results in excessively soluble copper
4) Its use at high temperatures and in dry weather.
5) The application of copper-based formulations at certain stages of a plant’s life cycle can cause phytotoxic effects, as many plants are sensitive to such compounds, even at low concentrations, such as during their flowering period.
So, copper is not a ”biological” or ”ecological” material, but a necessary evil. Let’s keep in mind every time we spray that the material that falls to the ground will add to what has fallen in previous years, and the total accumulation will burden the land we cultivate.
Christos Savvidis
