**3. Copper in horticultural environment**

In the context of metal and environment emphasis has to be laid on a complex system which embraces relations among soil characteristics, plant necessities and human expectations. Copper and its different substances constantly traverse from one to the other stage of this

**Characteristic Attribute / Value** 

Category transition metal

Atomic weight 63.546 gmol−<sup>1</sup>

Density (liquid density at m.p.) 8.94 gcm−3 (8.02 gcm−3) Boiling 2562 °C (2835 °K) Heat of fusion 13.26 kJmol−<sup>1</sup>

Specific heat capacity (25 °C) 24.440 Jmol−1K−<sup>1</sup>

Crystal structure face-centred cubic

Oxidation states +1, +2, +3, +4 (mildly basic oxide)

Copper has been part of the human civilisations since ancient times up to present days, its first records date back 5,000 and 6,000 years in the past. More specified utilization of copper as metal was achieved in the time of Sumerians and Chaldeans in Mesopotamia, who developed considerable skills in copper handling. Copper fabricated in Mesopotamia was quickly introduced to the the Egyptian Empire where its use flourished thousands of years. These peoples used copper for the fabrication of different jewels, ornaments, but also in the fields of armament and tools. They soon realized that pure copper, because of its softness, is not suitable for shaping tools used in agriculture, cultivation. Later, in the era of the Romans other metals, especially iron and bronze as the main metals in weaponry, gained in importance. In that time copper was first used also for architectural intentions, what can be

In Medieval times the use of copper additionally decreased because of the turbulent events in Europe involving the French, Germans, Burgundians, Anglo-Saxons and many more; when bronze had given off its place largely to iron in context of paramount agriculture, but also wars were common in that time. In the context of currency, silver took over the main role, although

The copper boom could be linked to immense changes in the time of industrial revolution, when the demand for better raw materials rapidly increased. In the 17th and 18th Centuries massive copper mines and smelting furnaces were exploited and erected to produce several

Nowadays copper presents an important metal, what is undoubtly affirmed by its worldwide annual production of around 5 million tons. Many branches of modern technology use and include copper in their products, especially in the electrical, architectural and chemical industry as well as medicine. The biggest copper sources are located in Chile, USA, Indonesia,

In the context of metal and environment emphasis has to be laid on a complex system which embraces relations among soil characteristics, plant necessities and human expectations. Copper and its different substances constantly traverse from one to the other stage of this

some copper coins were occasionally hammered in Mercia during the 8th Century.

Phase solid Atomic number 29

Table 1. Chemical and physical properties of copper (Cu)

witnessed on the roof sheathing of the Pantheon.

hundreds of tons of pure copper per week.

**3. Copper in horticultural environment** 

Australia and China, where it became the most exported metal.

**2. Copper in past** 


system where they are ascribed many roles and have different functions, which is rendered possible with permanent transformation.

Table 2. Average content of metals (mg kg-1) in different soil and stoneware types (Ross, 1994; Šajn et al., 1998)

Copper as a microelement effects the characteristics of the soils, that are also its preliminary source, while its content depends on parental matter (Table 2). Copper reaches the soil almost exclusively in divalent form (Cu2+ ions) incorporated in minerals but also bound with soil organic matter. Reed & Martens (1996) reported the specifically adsorption of Cu to carbonates, soil organic matter, phyllosilicates, and hydrous oxides of Al, Fe, and Mn. Usually it is dissolved in soil solutions as Cu2+ or as an organic complex adsorbed to inorganic and organic negatively charged groups. The presence of Cu2+ ions in soil solutions decreases with increasing pH, whereas Cu complexes are less dependent on soil pH. Cu2+, compared to other divalent cations (Ni, Co, Zn, Mn, Mg), has a strong affinity to soil organic matter, its concentration in soil ranges from 1 x 10-5 to 6 x 10-4 mol m-3, what is controlled by Cu adsorption to organic and inorganic soil particles. Because of this the transition of Cu in deeper soil layers rarely occurs, however it can be promote by soil cultivation (deep ploughing) and by decreasing soil pH to 5.5-6.5, at which values the mobility of Cu increases (Fig. 1).

Fig. 1. The mobility of metals according to pH of soil

Copper in Horticulture 261

paradox, as Cu is in this cultivation practices beside sulphur the only permitted element in

Fig. 3. Differences in total copper accumulation (mg kg-1) according to soil depth (cm) and to

The essentiality of copper for optimal growth and reproduction in higher plants is largely due to its occurrence as a constituent of several proteins (copper protein/enzyme), which regulate many essential biochemical reactions in plants. Sandmann & Böger (1983) report three different forms of proteins where copper plays an important component (Cu-proteins): blue proteins (plastocyanin; without oxidase activity) with function in one-electron transfer, non-blue proteins which represents peroxidises and oxidize monophenols to diphenols, and multicopper proteins with at least four Cu-atoms per molecule, which acts as oxidases (ascorbate oxidase and diphenol oxidase). Consequently Cu plays an essential role at the

a. photosynthesis and respiration: both can be inhibited by Cu deficiency, as Cu-enzymes catalyse or activate various steps in these processes. Cu is required for the formation of chlorophyll and other thylakoid constituents - with chlorosis being one of the symptoms of copper deficiency - Cu is particularly involved in photosynthesis as a component of ribulose-disphosphate carboxylase, while at respiration it is present as the copper enzyme

cytochrome-c-oxidase, where its deficiency may reduce respiration rates.

vineyards age. Means and standard errors are presented (Rusjan et al., 2007).

**3.1 Copper and horticultural plants** 

following physiological and other functions:

pathogen controlling.

The bounding and bioavailability of Cu depends also on the concentration of other elements in soil, where an antagonistic effect is observed between N, P and Mo : Cu and between Cu : Zn, Mn, while synergism has not been reported yet (Fig. 2).

Fig. 2. Synergism (blue) and antagonism (red) among elements in soil

Beside the parental matter of soils the significant "sources" of copper are agriculture (spraying, fertilisation), industry (metallurgy, pharmacy, mining etc.) and cities and roads, which together can be denoted as pollutants. Intensive agricultural practices based on substantial use of copper compounds in fungicides have in the last 200 years lead to copper accumulation in soils, especially in traditional horticultural areas (Fig. 3), like some winegrowing regions in France, Northern Italy, Germany an many more, where copper contents in soils are likely to reach many hundreds ppm. Long time use of Cu preparations leads to the accumulation of copper, where many data from viticultural area has been already reported (France: Bordeaux 800 mg kg-1, Alsace, Burgundy and Champagne 400 - 500 mg kg-1; Italy: Valle d'Aosta 300 mg kg-1, Lombardia 260 mg kg-1, Trentino Alto Adige 161 mg kg-1, Piemonte 90 mg kg-1, Tuscany 34 mg kg-1 etc. (Brun et al., 1998) and Slovenia 5- 150 mg kg-1 (Rusjan et al., 2007)). Rusjan et al. (2007) reported that Cu concentration in soils in horticultural environments with intensive cultivating practices increases with years, especially in the upper soil layers (< 20 cm) reaching more than 150 mg kg-1 after 30 years of permanent Cu usage. The accumulation of exceeded concentrations of Cu in soils leads to the perish of flora and fauna in the soils; however the greatest concerns are residuals of Cu in food (vegetable and fruit).

In the sense of a greater awareness of environmental issues European Union member states and some countries in particular are adopting many regulations to decrease the use of copper compounds in agriculture, where its permitted annual quantity does not exceed 5 kg of pure Cu per hectare. An increase of environmentally-sound cultivation practices is frequently mentioned as the most significant reason of excessive Cu pollution, leading to a

The bounding and bioavailability of Cu depends also on the concentration of other elements in soil, where an antagonistic effect is observed between N, P and Mo : Cu and between Cu : Zn,

Mn, while synergism has not been reported yet (Fig. 2).

Fig. 2. Synergism (blue) and antagonism (red) among elements in soil

in food (vegetable and fruit).

Beside the parental matter of soils the significant "sources" of copper are agriculture (spraying, fertilisation), industry (metallurgy, pharmacy, mining etc.) and cities and roads, which together can be denoted as pollutants. Intensive agricultural practices based on substantial use of copper compounds in fungicides have in the last 200 years lead to copper accumulation in soils, especially in traditional horticultural areas (Fig. 3), like some winegrowing regions in France, Northern Italy, Germany an many more, where copper contents in soils are likely to reach many hundreds ppm. Long time use of Cu preparations leads to the accumulation of copper, where many data from viticultural area has been already reported (France: Bordeaux 800 mg kg-1, Alsace, Burgundy and Champagne 400 - 500 mg kg-1; Italy: Valle d'Aosta 300 mg kg-1, Lombardia 260 mg kg-1, Trentino Alto Adige 161 mg kg-1, Piemonte 90 mg kg-1, Tuscany 34 mg kg-1 etc. (Brun et al., 1998) and Slovenia 5- 150 mg kg-1 (Rusjan et al., 2007)). Rusjan et al. (2007) reported that Cu concentration in soils in horticultural environments with intensive cultivating practices increases with years, especially in the upper soil layers (< 20 cm) reaching more than 150 mg kg-1 after 30 years of permanent Cu usage. The accumulation of exceeded concentrations of Cu in soils leads to the perish of flora and fauna in the soils; however the greatest concerns are residuals of Cu

In the sense of a greater awareness of environmental issues European Union member states and some countries in particular are adopting many regulations to decrease the use of copper compounds in agriculture, where its permitted annual quantity does not exceed 5 kg of pure Cu per hectare. An increase of environmentally-sound cultivation practices is frequently mentioned as the most significant reason of excessive Cu pollution, leading to a paradox, as Cu is in this cultivation practices beside sulphur the only permitted element in pathogen controlling.

Fig. 3. Differences in total copper accumulation (mg kg-1) according to soil depth (cm) and to vineyards age. Means and standard errors are presented (Rusjan et al., 2007).

#### **3.1 Copper and horticultural plants**

The essentiality of copper for optimal growth and reproduction in higher plants is largely due to its occurrence as a constituent of several proteins (copper protein/enzyme), which regulate many essential biochemical reactions in plants. Sandmann & Böger (1983) report three different forms of proteins where copper plays an important component (Cu-proteins): blue proteins (plastocyanin; without oxidase activity) with function in one-electron transfer, non-blue proteins which represents peroxidises and oxidize monophenols to diphenols, and multicopper proteins with at least four Cu-atoms per molecule, which acts as oxidases (ascorbate oxidase and diphenol oxidase). Consequently Cu plays an essential role at the following physiological and other functions:

a. photosynthesis and respiration: both can be inhibited by Cu deficiency, as Cu-enzymes catalyse or activate various steps in these processes. Cu is required for the formation of chlorophyll and other thylakoid constituents - with chlorosis being one of the symptoms of copper deficiency - Cu is particularly involved in photosynthesis as a component of ribulose-disphosphate carboxylase, while at respiration it is present as the copper enzyme cytochrome-c-oxidase, where its deficiency may reduce respiration rates.

Copper in Horticulture 263

The toxicity caused by copper is a rare phenomena in horticulture, especially where the control of soil pH is controlled and regulated. The most frequent symptoms on plants in terms of excessive copper concentrations are inadequate, obstructed shoot and root growth and vigour, whereas also chlorosis frequently appears on leaves. The excess of copper in soil could be controlled with dosing of lime in soils to increase of pH over 6.5. The effect can be intensified by adding of Fe (iron) because of its antagonism relationship with Cu. The Cu concentrations over 20 mg kg-1 in dry matter of plant tissues (parts), and over 30 mg kg-1 in soils can cause toxicity, dependent on plant species, age and part (organ), cultivation practices, environmental conditions and the condition of the plant (infections). The resistance to Cu toxicity may include immobilization or exclusion of the metal in/from root tissues, formation of complexes among organic acids and proteins, but also adaptation of

First records of the agricultural use of Cu compounds date back to 1761, when the discovery of the antibacterial effects of copper sulphate preparations used on seed grains set up

The most important breakthrough of copper use in viticulture though was undoubtedly in 1880, when the French scientist Pierre-Marie Alexis Millardet from the Bordeaux district in France chanced to notice that those vines, which had been daubed with a paste of copper sulphate and lime in water, in order to make the grapes unattractive to passers-bys and as well as animals, appeared less affected by downy mildew. Only five years later in 1885 Millardet announced his discovery to the world, a cure for the dreaded mildew through the application of the mixture of copper sulphate, lime and water, up to the present day called the Bordeaux mixture. Additionally to the Bordeaux mixture, but including copper sulphate and sodium carbonate (soda crystals) the so called Burgundy mixture appeared few years

At that time the Bordeaux and Burgundy mixtures became indispensable fungicides against various fungus diseases of plants, where the prevention enhanced with the proper application, means an appropriate timing and correct use of the fungicide. Consequently, as standing for a successful plant protection method up to the present days, many thousands

The days of prosperity of the production of fungicides based on copper compounds were in the middle of 20th century when many different chemical combinations with copper were applied. In the last decades and these days pharmaceutical corporations have been fabricating copper based fungicides in soluble forms of sulphates, oxychlorides, acetates, carbonates, oleates, silicates, ohydroxides etc. Most compounds of copper adopt the oxidation states Cu+ and Cu2+, respectively called cuprous and cupric. Their efficiency against fungal and bacterial infections is mostly reflected in their capability to retain on the plant surface, but not by the number of applications or the concentration of the agens in the fungicide. Copper is also biostatic which means that bacteria cannot grow on surfaces treated with it. Copper barriers can range from copper tape made as a slug barrier to more decorative hammered copper sheeting. Any copper that leaches into the soil around the plants is non-toxic and will not adversely affect the plants or people consuming the

enzyme mechanisms (Lepp, 1981; Woolhouse and Walker 1981).

**4. Copper in agricultural use: Sustainable horticulture** 

further standards in cultivation practices for the following decades.

of tons of copper are used annually in agriculture all over the globe.

later.

vegetables and fruits.


The uptake of copper in the form of Cu2+ is done after the metal ion dissociation from the organically complex molecules in soil and it can be enhanced by fungi associated with roots, also known as vesicular-arbuscular mycorrhizae. Research on the interaction between phosphorus and copper contents in soil has already been done; phosphorus improves root growth and thus increases copper absorption, therefore the fertilisation should be adapted at presence or absence of mycorrhizae.

Not only the deficiency of copper contents but also its sufficiency (excess) causes irreversible consequences on plant growth, its cultivation and with that quality (Fig. 4).

Fig. 4. Effects of copper availability (deficient, sufficient and excessive) on growth and yield of plant

b. lignifications and phenol metabolism: copper deficiency can significantly reduce the activity of the phenol oxidases which are involved in the lignin synthesis, leading to formations of rather weak tissues and the distortion of leaves and stems. Cu presence affects the synthesis of phenol compounds which inhibit cell elongation. Cu intensifies oxidation of phenol compounds to chinons, wound healing and pigment

c. regulation of auxins (growth): shortage of auxin is frequently caused by copper deficiency, resulting in a lack of germination. The monophenol compounds control the

d. reproduction: deficiency of copper leads to the production of higher polyphenols contents (diphenols) which inhibit the auxin oxidase and consequently the auxin accumulation in anthers. The shortage of auxin causes the formation of a large mass of cellular material, which eventually fills the cavity normally occupied by the pollen

The uptake of copper in the form of Cu2+ is done after the metal ion dissociation from the organically complex molecules in soil and it can be enhanced by fungi associated with roots, also known as vesicular-arbuscular mycorrhizae. Research on the interaction between phosphorus and copper contents in soil has already been done; phosphorus improves root growth and thus increases copper absorption, therefore the fertilisation should be adapted

Not only the deficiency of copper contents but also its sufficiency (excess) causes irreversible consequences on plant growth, its cultivation and with that quality (Fig. 4).

Fig. 4. Effects of copper availability (deficient, sufficient and excessive) on growth and yield

grains and consequently renders the pollen grains sterile (Alloway et al., 1985).

activity of enzyme auxin oxidase, but diphenols inhibit it.

formation.

of plant

at presence or absence of mycorrhizae.

The toxicity caused by copper is a rare phenomena in horticulture, especially where the control of soil pH is controlled and regulated. The most frequent symptoms on plants in terms of excessive copper concentrations are inadequate, obstructed shoot and root growth and vigour, whereas also chlorosis frequently appears on leaves. The excess of copper in soil could be controlled with dosing of lime in soils to increase of pH over 6.5. The effect can be intensified by adding of Fe (iron) because of its antagonism relationship with Cu. The Cu concentrations over 20 mg kg-1 in dry matter of plant tissues (parts), and over 30 mg kg-1 in soils can cause toxicity, dependent on plant species, age and part (organ), cultivation practices, environmental conditions and the condition of the plant (infections). The resistance to Cu toxicity may include immobilization or exclusion of the metal in/from root tissues, formation of complexes among organic acids and proteins, but also adaptation of enzyme mechanisms (Lepp, 1981; Woolhouse and Walker 1981).
